Problem FTB Academy Server, cant interact with blocks of people on the same team even after unclaiming chunks

[Erbs]

I was playing with some friends on the FTB Academy Public Server and added them to my team (and even made them admins of it), but some time after claiming a chunk, it tells them they don't have permission to access stuff in a about 10x10 area (not a complete chunk and also not connected to chunk borders). Unclaiming the chunk, unclaiming all chunks, switching ownership of the team, kicking them from the team and making them allies instead all didnt change this fact.