Thanks for monitoring this issue also.
My app said "delete all unselected content" I unchecked it and pressed 'sync now'. It just said 'sync incomplete'
I then unchecked 'delete unselected content copies and pressed 'sync now'. That worked - it started syncing again. It downloaded about 100 tracks then stopped. When I tried to sync again it said "Connecting to wifi network. Please wait."
It hung on that screen for hours. I restarted the phone - I restarted MM on the PC but it is still just sat on that message, "Connecting to wifi".
... three hours later it started syncing. So I presume while it said it was 'connecting to wifi', it was actually processing files? It might be an idea to change the message so people understand what is actually happening and don't repeatedly restart the device thinking the wifi is off. Maybe a message that, 'depending on the quantity of tracks in your library, this processing may take 3-4 hours"....
It stopped syncing several times. I restarted the sync each time and it connected quickly until eventually it crashed and I got the error here: https://1drv.ms/u/s!AoM1UrOaoKUMj5w2P-L1dKs9rWVVOg
I have sent the log.
After that I got the message "connection failed" each time I tried to sync. I restarted the device and got the "Connecting to Wifi" message again. It has been more than an hour on this message, not letting me progress further.
The next day I started again and the syncing began fine. I had about 1380 tracks to download. The app would download 300-400 and then stop. when I synced again, it said it had about 1200 tracks to download. This happened a few times. One time it downloaded 600 tracks before stopping. When I restarted I was back to 1000 tracks left to download. Next it downloaded about 800 tracks and stopped. When started again it had 1386 tracks left to download.
So the app is obviously not performing an accurate count of tracks left to download each time it syncs or, does it have a maximum of 1386 tracks it can download at one time? It is not creating duplicates. The downloads are the next tracks in alphabetical order.