in last 2 days I had the same problem with the same user: he joined my room, but he was not really in that one where I was with other people, even if URL was the same.
Yesterday we fixed opening a private window of Chrome.
Certainly his name has a single quote ’
Do you mean in his nickname? No, he uses name and surname without any ’ or special characters
I have verified that this problem is resolved a while ago. But better your subject is another reality. jitsi is currently looking for the development of subgroups allowing to swap in a single room. see https://platform-euhack21.bemyapp.com/#/event
Also another user told me she randomly has similar issue, after 4 or 5 times of disconnections she could join the room some days ago. We use always the same room on https://meet.jit.si