I would say that the colony has a disease problem, nosema or the viruses that bees are infected with. The queens can be infected and the bees keep trying to replace them. Try giving the colony a couple of frames of sealed and emerging brood and a frame of unsealed brood from one of your other colonies. If you have a capped queen cell it speeds up the process. Your nurse bees can infect the larvae so nurse age bees from another colony may help solve the problem.