Hive B has a wax moth problem - or they're unusually good at coping with it. I'm betting that it's a problem. I'll know when it's warm enough to have a look inside.
I have found 4 wax moth larvae on the removable floor of the hive. I've been keeping the floor clear of debris so I don't think they hatched on the floor, unless there is more debris that I can't see.