This happens to me frequently, started having to refresh every battle, but it kept happening even more (more reels makes it more likely) , so I had to stop playing.
The game becomes laggy in full screen, I think because my system resolution on my laptop is high.
But, I'm not sure what you mean by full screen and then minimise? Click the full-screen button, then do Windows+down to minimise? It didn't seem to help.
