As far as I can see, you have joined someone else’s Plex Home, back in August. (I assume you only intended to accept his media sharing offer, but you were inadvertently invited into the Home as well. The user name of that user starts with “B”.)
While this has almost no effects for you personally, it will destroy your own Plex Home. And therefore all users who were previously part of your own Home are now “homeless”, so to speak. They won’t be able to profit from the benefits of your Plex Pass anymore.
In order to solve this, you need to:
- leave the current Home https://support.plex.tv/articles/203888038-how-do-i-leave-a-plex-home/
- stop and restart both your Plex server and your Plex client(s)
- inspect the Plex Home settings page and see if you now can invite users again
