I'm at a friendly gym and I trained successfully twice in a row. On my third attempt the wonky GPS slightly moved my trainer outside the gym radius immediately ending the battle.
I moved myself closer so that this wouldn't happen, but now whenever I attempt to train it gets as far as the "GO" screen shown below:
Then it immediately exits back to the Gym. I have no idea why. As per my question here, you should be able to train as many times as you want without cool down.
I've tried hard restarting, but I'm curious if this is a known bug or not because I've not seen anything about it.