[Bugs] cannot claim gym I took down "gym is under attack" message despite the gym being colorless

I took down a Team Mystic gym but I was unable to claim it after I defeated the gym. It kept telling me that the gym was under attack despite the fact that the gym was now colorless. No matter how many times I tried to throw a Pokémon into the gym, it told me that it was under attack.

Eventually Team Mystic just reclaimed their gym while I was getting that gym under attack message. So obviously others are not getting that message