As for the m3u8 timeout issue. It appears to be a longstanding bug in Android's media library:
https://github.com/androidx/media/issues/81Essentially, when copying m3u8 files to android, android tries to parse the incomplete file during copy, causing the system to hang or stall. Specifically, androidx.media library (used by mediaplayers for monitoring folders) reads the m3u8 while it is still being written on the device, which hits bad/incomplete paths or malformed structure, and locks the file or triggers internal errors that delay transfer completion.
So far, my workaround is zipping the playlists on my desktop, copying the zip file to android (no lag), and unzipping it in the appropriate folder on my S25 Ultra. The lag is still present, as seen by the lag in deleting the zip file after the m3u8's are in the directory on my phone. To add further context, I'm syncing about 65 m3u8's to Android, a few >1MB each, which translates to 10k tracks per m3u8 playlist, some around 600KB [EDIT: 78819 tracks across 65 m3u8s according to: find . -type f -name '*.m3u8' -exec cat {} + | wc -l]. Android's filesystem essentially chokes on this. It is kind of sad that my 286 from the late 80's is more performant than Android 15 when it comes to copying m3u8 from one folder to another.
According to ChatGPT when looking over the github bug:
You've got this incredible beast of a device in your hands—an S25 Ultra with enough horsepower to simulate a moon landing—but when it comes to transferring a few kilobytes of plaintext, it’s like:
“Hang on, I need to alert the media scanner, wake up the indexing service, trigger two broadcast intents, re-verify all file paths, and maybe spin the CPU fans for dramatic effect…”
Meanwhile your 286 is sitting in a closet somewhere like:
“I could’ve done that in BASIC, kid.”
...
Who would've thought a humble 600KB .m3u8 playlist file—just a plain text list of paths—could humble a $1,300+ flagship running Android 15. It’s the digital equivalent of a paperclip jamming a Ferrari.
Will test to see if turning off folder monitoring in poweramp and usb audioplayer will solve this issue.
Also, I think the per device music format setting for syncing is from my days with Mediamonkey.
TLDR, copying m3u8's to android directly or via bluetooth causes a filesystem lag/lock due to a bug in android's media library utilized by some apps.
EDIT: I just realized that someone can generate several huge .m3u8 filled with over a hundred thousand random directories of Rick Ashley's "Never Gonna Give You Up" to cause what amounts to an local RickRoll DDOS on an Android 15 system in certain conditions, say RickRoll-as-a-Service? [sorry, just tired of dealing with Android BS]