I’ve found that Mosaic is occasionally “forgetting” the contents of playlists I’ve created. Just now when I fired up the system the playlist names are there but the contents are random tracks and not those that I created.
And, yes, I rescanned the songs and playlists on my Melco. I also, completely shut down the Bartok. No help. My most recently created playlists (created yesterday) are intact but all the ones before are garbage.
This is a known issue and a fix is hoped for in the next version of Mosaic ( which is awaited daily 
). See this thread from the archives:
Many thanks, Pete. In a sense relieved it’s not just me, but that would have been simpler to correct. I can’t wait for the Mosaic update. (The Melco and the Bartok sound fantastic together via Ethernet cable - many thanks for the heads up.)
I suppose a real brute force approach would be to take advantage of the 6 TB available on the Melco and make copies of tracks to create separate ‘playlist’ folders - editing metadata suitably.
I’m using 14.2(18B92) on an iPad and the Bartok has incorrect playlists. I’ve bitten the bullet time-wise and brute force copied files and edited metadata to create playlists. It would still be nice to be able to do this on the fly.