Today I tried to login with a second device for the first time. That didn't work out quite well. After entering the PIN or login key I get a small dialogue box flashing for a split second after which the site reloads and I'm still not logged in. I made a screenshot of said dialogue:
The line with the checkbox next to it reads "Don't allow more dialogues from this site" (or something like that) in German (the localisation of that PC).
this was a regression, now fixed!