[M] does indeed indicates that a track or album originates from a Master recording.
Though BubbleUPnP does not support HiRes MQA and the maximum is FLAC 44.1 kHz / 16 bit (CD Quality).
But that FLAC might have been generated from a Master recording (rather than the usual CD), which the app indicates as such.
Now, why it does not play is something else.
To which renderer are you playing to ?
So I can have a look, can you send me a log file, attempting to play a problematic track to your renderer
- launch the app
- go into More > Gear icon > Control
- Enable "logging to file" (at the end of the page).
- IMPORTANT: Exit the app (More > "X" bottom left icon)
- restart the app
- attempt to play a problematic track to your renderer
- exit the app
- email me (
bubblesof...@gmail.com) the files found on internal storage:
On Android 10 and below:
/Android/data/com.bubblesoft.android.bubbleupnp/log.txt
/Android/data/com.bubblesoft.android.bubbleupnp/prev_log.txt (if present)
On Android 11 and higher:
/Downloads/com.bubblesoft.android.bubbleupnp_log.txt
/Downloads/prev_com.bubblesoft.android.bubbleupnp_log.txt (if present)
You can access them with a file manager app and share them to your email app for sending them.
IMPORTANT: Make sure to not restart BubbleUPnP until you have sent or saved the log file as it is overwritten on app startup.