Bumping this old report as it is still relevant + some additional information.
Players can recognize and "fix" this bug by themselves.
How to check if you're bugged:
When someone goes into a portal to/out of the mini bosses, every player would normally get teleported in/out as well regardless of where they currently are on the map. IF you're bugged, only the player that went into the portal gets teleported.
How to "fix":
Someone has to die (not a joke). Die and revive (doesn't matter if you use a feather or revive from an Invoker) to fix it.
Alternatively: the fellowship leader can leave. Wouldn't recommend this option though x)