I have added some debug code to 0.3.3
can you run the sync without granting permission and capture the log
and then run again and grant permission and capture the log again
As requested with MB Wi-Fi sync v0.3.3
LOG WITHOUT PERMISSIONS
16 Mar 2019 15:11:18 com.getmusicbee.musicbeewifisync.ErrorHandler logError
SEVERE: receiveFile [SM-A500FU, 6.0.1, 0.3.3] file=Playlists/WHISSEY.m3u: java.io.FileNotFoundException: /storage/6264-3230/Playlists/WHISSEY.m3u: open failed: EACCES (Permission denied)
16 Mar 2019 15:11:18 com.getmusicbee.musicbeewifisync.ErrorHandler logError
SEVERE: receiveFile [SM-A500FU, 6.0.1, 0.3.3] file=Playlists/RATED.m3u: java.io.FileNotFoundException: /storage/6264-3230/Playlists/RATED.m3u: open failed: EACCES (Permission denied)
16 Mar 2019 15:11:18 com.getmusicbee.musicbeewifisync.ErrorHandler logError
SEVERE: receiveFile [SM-A500FU, 6.0.1, 0.3.3] file=Playlists/RANDOM.m3u: java.io.FileNotFoundException: /storage/6264-3230/Playlists/RANDOM.m3u: open failed: EACCES (Permission denied)
16 Mar 2019 15:11:19 com.getmusicbee.musicbeewifisync.ErrorHandler logError
SEVERE: receiveFile [SM-A500FU, 6.0.1, 0.3.3] file=Playlists/ONLY ME.m3u: java.io.FileNotFoundException: /storage/6264-3230/Playlists/ONLY ME.m3u: open failed: EACCES (Permission denied)
16 Mar 2019 15:11:19 com.getmusicbee.musicbeewifisync.ErrorHandler logError
SEVERE: receiveFile [SM-A500FU, 6.0.1, 0.3.3] file=Playlists/OLDIES.m3u: java.io.FileNotFoundException: /storage/6264-3230/Playlists/OLDIES.m3u: open failed: EACCES (Permission denied)
16 Mar 2019 15:11:19 com.getmusicbee.musicbeewifisync.ErrorHandler logError
SEVERE: receiveFile [SM-A500FU, 6.0.1, 0.3.3] file=Playlists/CLASSICS.m3u: java.io.FileNotFoundException: /storage/6264-3230/Playlists/CLASSICS.m3u: open failed: EACCES (Permission denied)
16 Mar 2019 15:11:19 com.getmusicbee.musicbeewifisync.ErrorHandler logError
SEVERE: receiveFile [SM-A500FU, 6.0.1, 0.3.3] file=Playlists/RECENTS.m3u: java.io.FileNotFoundException: /storage/6264-3230/Playlists/RECENTS.m3u: open failed: EACCES (Permission denied)
LOG WITH PERMISSIONS
16 Mar 2019 15:13:08 com.getmusicbee.musicbeewifisync.ErrorHandler logInfo
INFO: grant [SM-A500FU, 6.0.1, 0.3.3] saved permissions:
16 Mar 2019 15:13:08 com.getmusicbee.musicbeewifisync.ErrorHandler logInfo
INFO: grant [SM-A500FU, 6.0.1, 0.3.3] 6264-3230:: /storage/6264-3230
16 Mar 2019 15:13:08 com.getmusicbee.musicbeewifisync.ErrorHandler logInfo
INFO: grant [SM-A500FU, 6.0.1, 0.3.3] perm uri=content://com.android.externalstorage.documents/tree/6264-3230%3A,mapped path=/storage/6264-3230,write=true,sd card=/storage/6264-3230
16 Mar 2019 15:13:08 com.getmusicbee.musicbeewifisync.ErrorHandler logInfo
INFO: grant [SM-A500FU, 6.0.1, 0.3.3] selected permission=content://com.android.externalstorage.documents/tree/6264-3230%3A
16 Mar 2019 15:13:11 com.getmusicbee.musicbeewifisync.ErrorHandler logInfo
INFO: grant [SM-A500FU, 6.0.1, 0.3.3] saved permissions:
16 Mar 2019 15:13:11 com.getmusicbee.musicbeewifisync.ErrorHandler logInfo
INFO: grant [SM-A500FU, 6.0.1, 0.3.3] 6264-3230:: /storage/6264-3230
16 Mar 2019 15:13:11 com.getmusicbee.musicbeewifisync.ErrorHandler logInfo
INFO: grant [SM-A500FU, 6.0.1, 0.3.3] perm uri=content://com.android.externalstorage.documents/tree/6264-3230%3A,mapped path=/storage/6264-3230,write=true,sd card=/storage/6264-3230
16 Mar 2019 15:13:11 com.getmusicbee.musicbeewifisync.ErrorHandler logInfo
INFO: grant [SM-A500FU, 6.0.1, 0.3.3] selected permission=content://com.android.externalstorage.documents/tree/6264-3230%3A
16 Mar 2019 15:13:19 com.getmusicbee.musicbeewifisync.ErrorHandler logInfo
INFO: grant [SM-A500FU, 6.0.1, 0.3.3] saved permissions:
16 Mar 2019 15:13:19 com.getmusicbee.musicbeewifisync.ErrorHandler logInfo
INFO: grant [SM-A500FU, 6.0.1, 0.3.3] 6264-3230:: /storage/6264-3230
16 Mar 2019 15:13:19 com.getmusicbee.musicbeewifisync.ErrorHandler logInfo
INFO: grant [SM-A500FU, 6.0.1, 0.3.3] perm uri=content://com.android.externalstorage.documents/tree/6264-3230%3A,mapped path=/storage/6264-3230,write=true,sd card=/storage/6264-3230
16 Mar 2019 15:13:19 com.getmusicbee.musicbeewifisync.ErrorHandler logInfo
INFO: grant [SM-A500FU, 6.0.1, 0.3.3] selected permission=content://com.android.externalstorage.documents/tree/6264-3230%3A
Regards: Freddy