[Gameplay] Ult CD not showing?

In my last game playing Kennan top, at the beginning of the last team fight my ult was off CD by both the green dot indicating to allies that my ult was up as well as on the action bar. However, upon diving the opposing team, and my ceaseless mashing of the button, it did not go off. To double check that it was not my keyboard I was able to ping that it still had a CD ~3sec, despite not having a cooldown on my own screen. I was able to use the ult after three seconds from pinging, but before that point it did not have a cooldown on my own screen.