Part 2 of 2...
Then I deleted an album and did another sync. This time MB said it was successful, but the FiiO immediately said it was cancelled. I did not hit 'Stop' nor did I touch the device after touching 'sync now.' Here's the error log which contains not only the log data posted above, but also the new data, which starts at line 193 (time 14:00:28)
2019-05-04: X5; 5.1.1; 0.7.2
13:53:38: startSync: preview=true,iteration=0
13:53:38: command: action=SYNC_START
13:53:38: tryStart: connecting /192.168.1.101, attempt=0
13:53:38: tryStart: connected
13:53:38: tryStart: hello=true,fromMB=true,custfiles=false,preview=true,dev=X5,2
13:53:38: syncDevice: root=/mnt/external_sd1,ignoreErrors=false,playlists=false,ratings=false,playcount=false
13:53:43: syncDevice: command=ShowResults
13:53:48: syncDevice: command=GetFiles
13:53:48: getFiles: Get: Music/, inc=true
13:53:52: syncDevice: command=GetFiles
13:53:52: getFiles: Get: Podcasts/, inc=true
13:53:53: syncDevice: command=GetFiles
13:53:53: getFiles: Get: Playlists/, inc=false
13:53:53: syncDevice: command=ShowPreviewResults
13:53:53: syncDevice: exit
13:53:58: startSync: preview=false,iteration=1
13:53:58: command: action=SYNC_START
13:53:58: tryStart: connecting /192.168.1.101, attempt=0
13:53:58: tryStart: connected
13:53:58: tryStart: hello=true,fromMB=true,custfiles=false,preview=false,dev=X5,2
13:53:58: syncDevice: root=/mnt/external_sd1,ignoreErrors=false,playlists=false,ratings=false,playcount=false
13:54:02: syncDevice: command=ShowResults
13:54:07: syncDevice: command=GetFiles
13:54:07: getFiles: Get: Playlists/, inc=false
13:54:07: syncDevice: command=ReceiveFile
13:54:07: receiveFile: Receive: Playlists/Zumba.m3u
13:54:08: syncDevice: command=ReceiveFile
13:54:08: receiveFile: Receive: Playlists/Yesterday, Today, Tomorrow.m3u
13:54:08: syncDevice: command=ReceiveFile
13:54:08: receiveFile: Receive: Playlists/Yes & No.m3u
13:54:08: syncDevice: command=ReceiveFile
13:54:08: receiveFile: Receive: Playlists/Wishing & Hoping.m3u
13:54:08: syncDevice: command=ReceiveFile
13:54:08: receiveFile: Receive: Playlists/Will & Won't.m3u
13:54:08: syncDevice: command=ReceiveFile
13:54:08: receiveFile: Receive: Playlists/Weather.m3u
13:54:08: syncDevice: command=ReceiveFile
13:54:08: receiveFile: Receive: Playlists/Walking & Running.m3u
13:54:08: syncDevice: command=ReceiveFile
13:54:08: receiveFile: Receive: Playlists/Up & Down.m3u
13:54:08: syncDevice: command=ReceiveFile
13:54:08: receiveFile: Receive: Playlists/Truth & Lies.m3u
13:54:08: syncDevice: command=ReceiveFile
13:54:08: receiveFile: Receive: Playlists/Trains, Planes & Automobiles.m3u
13:54:08: syncDevice: command=ReceiveFile
13:54:08: receiveFile: Receive: Playlists/Time.m3u
13:54:08: syncDevice: command=ReceiveFile
13:54:08: receiveFile: Receive: Playlists/The Wrecking Crew.m3u
13:54:08: syncDevice: command=ReceiveFile
13:54:08: receiveFile: Receive: Playlists/The Rolling Stones.m3u
13:54:09: syncDevice: command=ReceiveFile
13:54:09: receiveFile: Receive: Playlists/The Four Seasons.m3u
13:54:09: syncDevice: command=ReceiveFile
13:54:09: receiveFile: Receive: Playlists/The Commitments.m3u
13:54:09: syncDevice: command=ReceiveFile
13:54:09: receiveFile: Receive: Playlists/Temperature.m3u
13:54:09: syncDevice: command=ReceiveFile
13:54:09: receiveFile: Receive: Playlists/Tears.m3u
13:54:09: syncDevice: command=ReceiveFile
13:54:09: receiveFile: Receive: Playlists/Sweet Stuff.m3u
13:54:09: syncDevice: command=ReceiveFile
13:54:09: receiveFile: Receive: Playlists/Street Map.m3u
13:54:09: syncDevice: command=ReceiveFile
13:54:09: receiveFile: Receive: Playlists/Stop, Look, Listen.m3u
13:54:09: syncDevice: command=ReceiveFile
13:54:09: receiveFile: Receive: Playlists/Something.m3u
13:54:09: syncDevice: command=ReceiveFile
13:54:09: receiveFile: Receive: Playlists/Sleeping, Dreaming, & Waking.m3u
13:54:09: syncDevice: command=ReceiveFile
13:54:09: receiveFile: Receive: Playlists/Royalty.m3u
13:54:09: syncDevice: command=ReceiveFile
13:54:09: receiveFile: Receive: Playlists/Rolling Stone's 500 Greatest Songs.m3u
13:54:09: syncDevice: command=ReceiveFile
13:54:09: receiveFile: Receive: Playlists/Rivers, Creeks, Streams.m3u
13:54:09: syncDevice: command=ReceiveFile
13:54:09: receiveFile: Receive: Playlists/Right & Wrong.m3u
13:54:09: syncDevice: command=ReceiveFile
13:54:09: receiveFile: Receive: Playlists/R & R HoF Inductees.m3u
13:54:09: syncDevice: command=ReceiveFile
13:54:09: receiveFile: Receive: Playlists/Questions.m3u
13:54:09: syncDevice: command=ReceiveFile
13:54:09: receiveFile: Receive: Playlists/One-Hit Wonders.m3u
13:54:10: syncDevice: command=ReceiveFile
13:54:10: receiveFile: Receive: Playlists/O Canada.m3u
13:54:10: syncDevice: command=ReceiveFile
13:54:10: receiveFile: Receive: Playlists/Now & Then.m3u
13:54:10: syncDevice: command=ReceiveFile
13:54:10: receiveFile: Receive: Playlists/Non-lexical Vocables.m3u
13:54:10: syncDevice: command=ReceiveFile
13:54:10: receiveFile: Receive: Playlists/Night & Day.m3u
13:54:10: syncDevice: command=ReceiveFile
13:54:10: receiveFile: Receive: Playlists/Names.m3u
13:54:10: syncDevice: command=ReceiveFile
13:54:10: receiveFile: Receive: Playlists/Musical Map.m3u
13:54:10: syncDevice: command=ReceiveFile
13:54:10: receiveFile: Receive: Playlists/Muscle Shoals.m3u
13:54:10: syncDevice: command=ReceiveFile
13:54:10: receiveFile: Receive: Playlists/Money.m3u
13:54:10: syncDevice: command=ReceiveFile
13:54:10: receiveFile: Receive: Playlists/Mama Gimme Layla.m3u
13:54:10: syncDevice: command=ReceiveFile
13:54:10: receiveFile: Receive: Playlists/Madness.m3u
13:54:10: syncDevice: command=ReceiveFile
13:54:10: receiveFile: Receive: Playlists/Look! Up In The Sky!.m3u
13:54:10: syncDevice: command=ReceiveFile
13:54:10: receiveFile: Receive: Playlists/Ladies.m3u
13:54:10: syncDevice: command=ReceiveFile
13:54:10: receiveFile: Receive: Playlists/Joy of Trumpet.m3u
13:54:10: syncDevice: command=ReceiveFile
13:54:10: receiveFile: Receive: Playlists/Joy of Sax.m3u
13:54:10: syncDevice: command=ReceiveFile
13:54:10: receiveFile: Receive: Playlists/Joy of Keyboards.m3u
13:54:10: syncDevice: command=ReceiveFile
13:54:10: receiveFile: Receive: Playlists/Joy of Bass.m3u
13:54:10: syncDevice: command=ReceiveFile
13:54:10: receiveFile: Receive: Playlists/Humans.m3u
13:54:10: syncDevice: command=ReceiveFile
13:54:10: receiveFile: Receive: Playlists/Hey Oh.m3u
13:54:10: syncDevice: command=ReceiveFile
13:54:10: receiveFile: Receive: Playlists/Here, There, & Everywhere.m3u
13:54:11: syncDevice: command=ReceiveFile
13:54:11: receiveFile: Receive: Playlists/Hello Goodbye.m3u
13:54:11: syncDevice: command=ReceiveFile
13:54:11: receiveFile: Receive: Playlists/Happy & Sad.m3u
13:54:11: syncDevice: command=ReceiveFile
13:54:11: receiveFile: Receive: Playlists/Good & Bad.m3u
13:54:11: syncDevice: command=ReceiveFile
13:54:11: receiveFile: Receive: Playlists/Give or Take.m3u
13:54:11: syncDevice: command=ReceiveFile
13:54:11: receiveFile: Receive: Playlists/George Harrison.m3u
13:54:11: syncDevice: command=ReceiveFile
13:54:11: receiveFile: Receive: Playlists/Funk.m3u
13:54:11: syncDevice: command=ReceiveFile
13:54:11: receiveFile: Receive: Playlists/Fools.m3u
13:54:11: syncDevice: command=ReceiveFile
13:54:11: receiveFile: Receive: Playlists/Family.m3u
13:54:11: syncDevice: command=ReceiveFile
13:54:11: receiveFile: Receive: Playlists/Falsetto.m3u
13:54:11: syncDevice: command=ReceiveFile
13:54:11: receiveFile: Receive: Playlists/Edible Arrangements.m3u
13:54:11: syncDevice: command=ReceiveFile
13:54:11: receiveFile: Receive: Playlists/Dynamic Duos.m3u
13:54:11: syncDevice: command=ReceiveFile
13:54:11: receiveFile: Receive: Playlists/Do & Don't.m3u
13:54:11: syncDevice: command=ReceiveFile
13:54:11: receiveFile: Receive: Playlists/Distinctive Voices.m3u
13:54:11: syncDevice: command=ReceiveFile
13:54:11: receiveFile: Receive: Playlists/Devil or Angel.m3u
13:54:11: syncDevice: command=ReceiveFile
13:54:11: receiveFile: Receive: Playlists/Dead or Alive.m3u
13:54:11: syncDevice: command=ReceiveFile
13:54:11: receiveFile: Receive: Playlists/Days of the Week.m3u
13:54:12: syncDevice: command=ReceiveFile
13:54:12: receiveFile: Receive: Playlists/Current Favorites.m3u
13:54:12: syncDevice: command=ReceiveFile
13:54:12: receiveFile: Receive: Playlists/Comings & Goings.m3u
13:54:12: syncDevice: command=ReceiveFile
13:54:12: receiveFile: Receive: Playlists/Colors.m3u
13:54:12: syncDevice: command=ReceiveFile
13:54:12: receiveFile: Receive: Playlists/Cats & Dogs.m3u
13:54:12: syncDevice: command=ReceiveFile
13:54:12: receiveFile: Receive: Playlists/Can & Can't.m3u
13:54:12: syncDevice: command=ReceiveFile
13:54:12: receiveFile: Receive: Playlists/By the Ordinals.m3u
13:54:12: syncDevice: command=ReceiveFile
13:54:12: receiveFile: Receive: Playlists/By the Numbers.m3u
13:54:12: syncDevice: command=ReceiveFile
13:54:12: receiveFile: Receive: Playlists/Body Parts.m3u
13:54:12: syncDevice: command=ReceiveFile
13:54:12: receiveFile: Receive: Playlists/Big & Little.m3u
13:54:12: syncDevice: command=ReceiveFile
13:54:12: receiveFile: Receive: Playlists/Benjamin.m3u
13:54:12: syncDevice: command=ReceiveFile
13:54:12: receiveFile: Receive: Playlists/Beginnings, Middles, & Ends.m3u
13:54:12: syncDevice: command=ReceiveFile
13:54:12: receiveFile: Receive: Playlists/Before & After.m3u
13:54:12: syncDevice: command=ReceiveFile
13:54:12: receiveFile: Receive: Playlists/Beatles & Stones Covers.m3u
13:54:12: syncDevice: command=ReceiveFile
13:54:12: receiveFile: Receive: Playlists/Baseball.m3u
13:54:12: syncDevice: command=ReceiveFile
13:54:12: receiveFile: Receive: Playlists/Animals.m3u
13:54:12: syncDevice: command=ReceiveFile
13:54:12: receiveFile: Receive: Playlists/Anatomy of a Song.m3u
13:54:13: syncDevice: command=ReceiveFile
13:54:13: receiveFile: Receive: Playlists/All Work & Some Play.m3u
13:54:13: syncDevice: command=ReceiveFile
13:54:13: receiveFile: Receive: Playlists/All or Nothing.m3u
13:54:13: syncDevice: command=Exit
13:54:13: exitSync: fails=0
13:54:27: syncDevice: exit
14:00:28: ping: socket ok=/192.168.1.101
14:00:28: ping: hello=MusicBeeWifiSyncServer/1.0
14:00:28: ping: matched=/192.168.1.101,status=OK
14:00:32: startSync: preview=true,iteration=0
14:00:32: command: action=SYNC_START
14:00:32: tryStart: connecting /192.168.1.101, attempt=0
14:00:32: tryStart: connected
14:00:32: tryStart: hello=true,fromMB=true,custfiles=false,preview=true,dev=X5,2
14:00:32: syncDevice: root=/mnt/external_sd1,ignoreErrors=false,playlists=false,ratings=false,playcount=false
14:00:37: syncDevice: command=ShowResults
14:00:41: syncDevice: command=GetFiles
14:00:41: getFiles: Get: Music/, inc=true
14:00:47: syncDevice: command=GetFiles
14:00:47: getFiles: Get: Podcasts/, inc=true
14:00:48: syncDevice: command=GetFiles
14:00:48: getFiles: Get: Playlists/, inc=false
14:00:48: syncDevice: command=ShowPreviewResults
14:00:48: syncDevice: exit
14:00:53: startSync: preview=false,iteration=1
14:00:53: command: action=SYNC_START
14:00:53: tryStart: connecting /192.168.1.101, attempt=0
14:00:53: tryStart: connected
14:00:53: tryStart: hello=true,fromMB=true,custfiles=false,preview=false,dev=X5,2
14:00:53: syncDevice: root=/mnt/external_sd1,ignoreErrors=false,playlists=false,ratings=false,playcount=false
14:00:58: syncDevice: command=ShowResults
14:01:02: syncDevice: command=GetFiles
14:01:02: getFiles: Get: Playlists/, inc=false
14:01:02: syncDevice: command=ShowDeleteConfirmation
14:01:02: syncDevice: command=Exit
14:01:02: exitSync: fails=0
14:01:03: syncDevice: exit
I then restarted the FiiO and tried another sync but with the same results. The new log entries were added to everything that came before it, but for the sake of clarity, I'm only posting the results from this third attempt, which seems to have a lot more data than the similar failure at 14:00. This time it looks like it can't connect to the PC where MB lives.
14:26:58: ping: socket ok=/192.168.1.101
14:26:58: ping: hello=MusicBeeWifiSyncServer/1.0
14:26:58: ping: matched=/192.168.1.101,status=OK
14:26:59: startSync: preview=true,iteration=0
14:26:59: command: action=SYNC_START
14:26:59: tryStart: connecting /192.168.1.101, attempt=0
14:27:01: tryStart: java.net.SocketTimeoutException: failed to connect to /192.168.1.101 (port 27304) after 2000ms
14:27:01: libcore.io.IoBridge.connectErrno(IoBridge.java:169)
14:27:01: libcore.io.IoBridge.connect(IoBridge.java:122)
14:27:01: java.net.PlainSocketImpl.connect(PlainSocketImpl.java:183)
14:27:01: java.net.PlainSocketImpl.connect(PlainSocketImpl.java:456)
14:27:01: java.net.Socket.connect(Socket.java:882)
14:27:01: com.getmusicbee.musicbeewifisync.WifiSyncService$SynchronisationWorker.tryStartSynchronisation(WifiSyncService.java:277)
14:27:02: com.getmusicbee.musicbeewifisync.WifiSyncService$SynchronisationWorker.run(WifiSyncService.java:232)
14:27:02: java.lang.Thread.run(Thread.java:818)
14:27:02: worker: no connection for 192.168.1.101 - trying again
14:27:02: locate: search=192.168.1.
14:27:02: locate: exclude=116
14:27:02: ping: socket ok=/192.168.1.101
14:27:02: ping: hello=MusicBeeWifiSyncServer/1.0
14:27:02: ping: matched=/192.168.1.101,status=OK
14:27:02: tryStart: connecting /192.168.1.101, attempt=0
14:27:02: tryStart: connected
14:27:02: tryStart: hello=true,fromMB=true,custfiles=false,preview=true,dev=X5,2
14:27:02: syncDevice: root=/mnt/external_sd1,ignoreErrors=false,playlists=false,ratings=false,playcount=false
14:27:06: syncDevice: command=ShowResults
14:27:10: syncDevice: command=GetFiles
14:27:10: getFiles: Get: Music/, inc=true
14:27:11: startSync: preview=true,iteration=0
14:27:11: command: action=SYNC_START
14:27:11: tryStart: connecting /192.168.1.101, attempt=0
14:27:11: tryStart: connected
14:27:14: syncDevice: command=GetFiles
14:27:14: getFiles: Get: Podcasts/, inc=true
14:27:14: syncDevice: command=GetFiles
14:27:14: getFiles: Get: Playlists/, inc=false
14:27:14: syncDevice: command=ShowPreviewResults
14:27:14: syncDevice: exit
14:27:14: tryStart: hello=true,fromMB=true,custfiles=false,preview=true,dev=X5,2
14:27:14: syncDevice: root=/mnt/external_sd1,ignoreErrors=false,playlists=false,ratings=false,playcount=false
14:27:18: syncDevice: command=ShowResults
14:27:23: syncDevice: command=GetFiles
14:27:23: getFiles: Get: Playlists/, inc=false
14:27:23: syncDevice: command=ShowPreviewResults
14:27:23: syncDevice: exit
14:27:25: ping: socket ok=/192.168.1.101
14:27:25: ping: hello=MusicBeeWifiSyncServer/1.0
14:27:25: ping: matched=/192.168.1.101,status=OK
14:27:32: startSync: preview=true,iteration=0
14:27:32: command: action=SYNC_START
14:27:32: tryStart: connecting /192.168.1.101, attempt=0
14:27:32: tryStart: connected
14:27:32: tryStart: hello=true,fromMB=true,custfiles=false,preview=true,dev=X5,2
14:27:32: syncDevice: root=/mnt/external_sd1,ignoreErrors=false,playlists=false,ratings=false,playcount=false
14:27:36: syncDevice: command=ShowResults
14:27:41: syncDevice: command=GetFiles
14:27:41: getFiles: Get: Playlists/, inc=false
14:27:41: syncDevice: command=ShowPreviewResults
14:27:41: syncDevice: exit
14:27:50: startSync: preview=false,iteration=1
14:27:50: command: action=SYNC_START
14:27:50: tryStart: connecting /192.168.1.101, attempt=0
14:27:50: tryStart: connected
14:27:50: tryStart: hello=true,fromMB=true,custfiles=false,preview=false,dev=X5,2
14:27:50: syncDevice: root=/mnt/external_sd1,ignoreErrors=false,playlists=false,ratings=false,playcount=false
14:27:54: syncDevice: command=ShowResults
14:27:59: syncDevice: command=GetFiles
14:27:59: getFiles: Get: Playlists/, inc=false
14:27:59: syncDevice: command=ShowDeleteConfirmation
14:27:59: syncDevice: command=Exit
14:27:59: exitSync: fails=0
14:28:00: syncDevice: exit