Online Only Using Keyboard Input

I play on PC, and have a Xbox controller. Works fine. I play offline games or am in the menus, the game picks up my controller just fine. But sometimes, not every time, I go to play an online match and I cannot control my players.

I've realised that the input, for some baffling reason, has gone to my keyboard and there's no way to switch it back. It's only some of the time, and closing the game and restarting can fix it, but there's no fix in game. Which means that if this happens, I lose that online match. Unless I somehow learn to play the game with the keyboard.

Is there a fix for this?