Usually this means there was some kind of a connection issue—even if your device was still connected to Wi-Fi or data properly, that doesn’t mean that your opponent’s device didn’t suffer a connectivity problem. It’s definitely not a bot or hacking issue…some of us might venture to call it a connectivity bug, but I’m not sure I’d even go as far as saying that.
If my timer freezes, or I’m stuck on a screen where you can see the arena background but no timer, I usually close the app and reopen it. Sometimes I’m lucky enough to re-enter the battle before the timer’s finished running down to select my first dinosaur. I haven’t been having issues for some time, though.