Yeah it doesn't really make sense.
The word "Prohibitions" itself makes it kinda clear, it encompasses all the things that can prohibit a person from becoming a citizen, including knowing the language, knowledge of Canada, physical presence, legal issues, being a PR... So it usually turns green when everything else does, and in practice does so along with the last other element that wasn't green yet.
It's either a mistake from an agent and it will go back in progress, or the BC is indeed completed and should reflect in the tracker soon.