Cho R on cd without hit, R ping says it's up

So this has happened to me 3-4 times now (I think the first one occured shortly after the ult rework) I as Cho ult somebody who is about to die but someone else gets the kill and my ult goes on cooldown. Which is already a bit weird because as far as I know it is an instant point and click ability which does not have a cast or travelling time (feel free to correct me if I'm wrong on that point), so it should've either gotten me the kill or not gone off in the first place. My first thought always was that I might've misunderstood the ult and it really does have a small delay between cast and damage, so I pinged my ult to tell my teammates that it was on cd. This is where it gets really interesting because the chat said it was ready, even though my UI showed me that it was on full cd and I could not use it when I tried to. I am not sure if the ult was working as intended or if the ping was correct, all I know is that one of them was wrong.

As far as I remember the other champions involved were different each time when this happened and it was at least once on SR and at least once in ARAM I always forgot to make a screenshot so this is sadly all the information that I can provide

Good luck fixing it ^^