This shows up in the nightly 3.0.3 version as well as the lower versions.
Join a group chat
Right click on own name, select change nickname
Put in new name
Lose access to the MUC window/chat. Cannot see people chatting, cannot chat myself, none of the right click options work.
Leave the room, rejoin. It is completely blank and becomes completely non-responsive.
I think part of this same thing Spark 3.0 - Issue in MUC when changing names - #3 by JayMan6014
This is why I cannot have any users running any of the 3.0 versions. but it did show up in some of the most recent 2.0 versions before the 3.0 came out.