[Awen Moonshine]

That's a gym battling glitch. There's no way of fixing it other than coming out of the game and going back in again. If I remember right the glitch happens when you view a gym when it is being battled by someone else.

PokeGo is sadly still full of bugs and glitches and with the non-stop events even I've not been playing as much of late... :( I think when I finally get Mew I'll give up for good as it's just not as fun anymore...