[GAMEPLAY] Ult doesn't show it's on CD.

While being deleted by the enemy team , as per usual when you take a really stupid build as AP , I was in a moment of panic and decided to Ult to see if my chances of escaping would increase even slightly. I do so but my ult doesn't go off. The sound of the ultimate plays but there are no animations that I can see. I've seen this happen many times and just decided that it wasn't that big of a deal and likely not a bug since it just means that I died too quickly that I couldn't even cast the ability. (feelsbadman) I go on with my depressingly bad game and see an opportunity to engage and save one of my teammates with my ult that appeared to be available to cast. Next thing I know I'm smashing R and nothing happens and then I return to the ever depressing gray screen... My other abilities seemed to have worked except for my ult. I even try using it in fountain to see if it was just my keyboard ghosting but nothing happens. I ping the ability only to find out that it's on cooldown. I don't really understand how it could've been because there weren't any timers to show my how much time is left on the ability's cooldown and instead showed the ultimate's picture as if it were available to cast. All I recall doing was 1. being stunned by the enemy before 2.instantly ult'ing while also 3.instantly being deleted (and I mean -1000+ health in less than a second deleted).