Not sure if this reported already, but I noticed if you have a member who is in more than 1 group, only the 1st group you add them to is displayed in their user profile, the 2nd, 3rd, etc groups are not displayed.
Disallow user to quit a group
No built in way to do this right now, although I think it would be useful as a core option in the group settings, like
Disable join requests. Can you open an issue on our tracker?
If you don't want to wait till it's implemented one hacky way to do it is to use the hook
'action:group.leave'and add the user back to the groups they just left.