I'm also using a QNAP for my core. I use Control:PC for my interface and it's been a couple of months since I could add a Tidal album to my library. The search function for Tidal still works and I can listen to the tracks, but I no longer get album cover art. I can create Sooloos playlists with Tidal tracks in them and they play fine. The Tidal albums I had added to my library in the past still play and retain the album cover art. My work-around is to add a Tidal album to my Play queue and then create a Playlist.

As an added note, I removed Tidal from Control:PC just to see if I could sign back in. I waited a week and was able to sign back in with no problem.

QNAP, MS600, MS200, Anthem AVM 50v, B&W 804S, JL Fathom 113 (2)