Guardian Angel

In a match i recently had, I had purchased a Guardian Angel because I was dying a lot to Pantheon as Yasuo. It works as usual until at a stage in the game where I died right as it came off cooldown.... it immediately goes back on cooldown but doesn't revive me. This is only happened once and I will update if it happens again or if under the same circumstances it doesn't happen again and the bug didn't affect me too much as we did win that game but I would just like to point this out as it happened once today.