This is a very old issue that has been talked about enough (see Group Chat: mod and unmod broken), just wanted to open a new thread to ask if there are any plans to fix it.
Group chats are a bit of an abandoned feature, and getting incrementally more and more broken. They really just need a little bit of maintenance and they’d be fine again.
I know not that many people use group chats these days, but having this half broken feature on the site is a weird state of affairs.