That's quite a common 'bug', besides it's not really one. I have it very often, but it's nothing you can do to solve that.
For example, I have to update my android, and if it shows up while I'm in the game, the screen switch and the last entry will be active if I switch back to the game. Also can happens sometimes if you reload a save game. It's easy to solve, just click on attack button again (reload error sometimes) or restart the game (for control)
I cant click the attack button again. It stays red. To unstuck it, i have to go settings -> controller settings, quit Error that i cant only be changed in main menu, and go back to game. This helps until next time. This can be next fight or next hour. its ramdom.
Rebooting didnt do anything.