Thanks for the tip. Mine had been changed from Master to High. Shame on me, I didn't even notice!
Tidal updates - check streaming settings
Twice in the last 6 months, after Tidal updates to their app, the streaming setting reverted to a lower resolution playback. I had to manually change it back. With the most recent update, the HiFi display on the main page remained highlighted even though it wasn’t playing back at the HiFi rate. A false positive. Be sure to check the steaming menu every so often.