GA Tryndamere bug

Late game, I bought a Guardian Angel while I was playing Tryndamere. When I was in a fight and getting low, i used my ult; however when my ult wore off, my GA didn't proc. It showed that it was on cool-down, but no effect whatsoever. I noticed it happening, as well as the enemy team. I ended up selling the item (for a Last Whisper because dmg), because I didn't want it to happen again. Hope this problem gets fixed!