I've gotten a Tidal error saying being used on another device, even when I was sure I wasn't using it elsewhere. But then it turned out I actually was (had been using Tidal on other system and just muted and put into standby without actually stopping the tracks from playing). Make sure you don't just exit out of an app on another device, but actually stop the song from playing (or power down the device).
Not sure if that is the issue you have, but relating it since it could affect others reading this.
Not sure if that is the issue you have, but relating it since it could affect others reading this.