[GAMEPLAY] Sion-Decimating Smash (Q) and Unstoppable Onslaught (R) disable mid-match

I have had this issue in two different matches, where mid-match (approximately 10-20 minutes in) Sion's Decimating Smash (Q) becomes disabled, shortly followed by Unstoppable Onslaught (R) becoming disabled as well. I have tried rebinding the quick cast to different keys, but this has had no effect. When you press the chosen quick cast key you hear the usual noise (indicating that the game recognizes the input) but the ability does not activate. Clicking either ability with the cursor produces the same effect.