Katarina Ult Bug

So I recently started getting into Katarina again, as she's one of my favorite champions and I hadn't played her in a while, and I've run into a really weird issue. Maybe it's a bug, maybe it's just a mistake I'm making, but I think it's a bug. So I find that my ult as Kat has been randomly ending/canceling. It happens VERY often, though, which is what I find weird. Every 1 out of like 5 ults, the ult goes on without canceling itself. I'm not talking about cc, I'm not talking about anything like that, the ult just ends. Every time it either works or cancels itself, I don't do anything differently. I never move after my q e w r combo, but the ult will do damage for about .5 seconds and then just stop. Even when it does go one for the full duration, I do nothing differently, but it'll continue for the full duration. What I find that works EVERY time, is to cancel all my commands after I go in with the e w. For me, the key is "s." If I press s, it's the command that cancels everything. Like, if I'm starting an auto attack and then press s, the auto will stop and won't go off (unless I pressed it too late, but it will stop after that), it's that command (don't know what it's called, I'm sorry) (Jk I found out and the command is called "Player Stop Position"). Anyways, if I q e w and then press s and ult, the ult will go off. This may work, but it's very annoying to have to remember that each time and then execute it, plus it takes away time from me doing damage, but I mean chances are that the ult will only go off for that .5 seconds if I don't do it. I think the issue is that movement commands made before the q e w continue even after you shunpo, if that makes sense. So, like, before when I used to play kat, I would shunpo and that would cancel any previous movement commands. Now, it seems like there's a bug (maybe not, maybe this is intentional) where shunpo is no longer canceling movement commands once it goes off, and that in turn is making the ult cancel because the game is still trying to move you. I hope that makes sense, but what's really annoying is that this never happened before, which is what makes me think it's a bug. I hope someone has an answer.