[GAMEPLAY] R button does not do anything, have to click icon

I have an issue where clicking the R button does not do anything. In order to use my ultimate, I have to click the icon down at the bottom of the screen, which isn't practical. For example, I was playing Braum and died during a teamfight while trying to use my ult, whereas I might have been able to use it if I didn't have this problem.

I can't explain how to repeat this since I don't know why it came up. Also, I once tried turning the smart-cast on and off, with the same problem in each case. Any help is appreciated.

EDIT: Well, I've found out what was causing this problem - the hotkey for my ult had disappeared. Somehow it got turned off and my ultimate no longer had a hotkey, so I didn't get a response when I hit 'R'. All I had to do was turn it back on.