Hi,
After you get Sync incomplete use ⋮ -> About MediaMonkey -> Send Logs -> Write down log ID here and send it. It will tell us why it happens.

Also make sure you are using latest MMW and MMA Beta.

Both Android app and Win installation up-to-date.
Had been working fine but recently I get Sync is starting for AGES then it eventually says Sync Incomplete.
I have tried everything. Resinstalling MMA, removing latest additions to the Playlist I was syncing, etc.