It’s seems that’s there’s now a feature which tries to stop people abusing Pokemon gyms, by giving them a please try again later message when they try to use the gym. Conditions that mark you as a gym abuser are:
Leaving a fight early.
Drifting or of range of a gym during a fight.
It seems dumb to give people a button to leave a fight, then punish them with a please try again later message. Still, the please try again is only temporary, and lasts about 30 seconds.