Like you, I’ve had Cubase for years, although only run it on Mac for the last couple of years. Like you, Cubase 10.5 sometimes opens up on my machine as Cubase Artist 10.5. Sometimes when this happens I get licenser errors and the only way to come out of this is to force quit Cubase. Sometimes I don’t get elicenser errors but Cubase is running as Artist not Pro.
I reinstalled all my licences onto a different dongle - same intermittent issue. I always run maintenance on my elicenser regularly. Tonight I have just updated to the new licenser issued on 7th January and the problem has returned. Intermittently.