First of all, sorry if it has been asked already. I couldn't find anything similar, though.
I tried to attack a hostile gym and it worked fine until then. I also caught some Pokémon on my way there and collected a few Pokéstops. So my guess is, that the connection was fine.
Also the GPS positioning was good and I didn't get pushed out of the gym's range.
(The gym itself was at a main station, so it's a pretty busy place.)
The issue itself:
I could select the gym, tap on fight and select my combat Pokémon and start the fight with no issues. But as soon as the countdown for the first fight ended I got thrown back to the main menu of that gym and I had to tap on the fight button again. I haven't seen this before and it was only this one gym. There was another gym in the area, which I could use as intended (this was a friendly one, though).
Do I have to report that gym or was it just a temporary problem? If so, what kind of problem was it?
Update: I have collected several details about this using the classic method try and error. So far I got it reproduced even without any connection issues.
Narrowed down it can be caused by:
- GPS Problem (not server related)
- interrupted previous fight (app crash, etc)
- server issues