Game lockup, partying and anti cheat test
I was partying with someone who had the anti cheat test pop up. When I was solo there was no problem with the test, but the person didn't answer right away.
So the game let me as the party leader keep walking around, while for the other person they had the cheat test up and so they were not moving and they were still on the same screen.
The person answered their test, but the game disconnected them when they did. For me it looked like we were all still running around in game, but no monsters were attacking us as I ran around. It eventually disconnected me too.
It told me I was logged in already for the next 15 minutes as I tried to log in, and it did so for the other person in the party too.
So when the anti cheat test pops up in a party situation it creates a problem if the party leader keeps walking around and the other person doesn't answer right away (they didn't answer for like 10 seconds, I'm unsure of the amount of time that needs to go by before it causes a problem so far, I'll update this if I learn more about it).