Sion Gameplay bugged out

Was playing as Sion, most of the game went fine. But after I died in a teamfight towards the latter half of the game, I found myself unable to use my Q or my Ultimate with him. Sion could still use his other two abilities but I am not quite sure what locked them out for me exactly. It only happened at the end, and I'm confused why it hadn't happened before or why no matter what I did at the end it wouldn't activate.