I never had any problems with Tidal but since Roon 2.66 Roon logged out of Tidal already twice and each time I did not manage to login Tidal again for at least a day.
When I try to connect Roon with Tidal then Tidal confirms me in browser a successful connection but Roon reports an authentification error.
I have exactly the same issue. While the browser confirms the log in to be successful I see “authentication failed, please try again later” in Roon. It currently unusable for me.