Annie stun not working properly?

Ok so this has been going on for a very long time and I've found plenty of posts mentioning it but they are 9 months old posts and the issue is still here after all this time. I have noticed that something was wrong with annies stun, especially with tibbers cause sometimes I would throw tibbers with pyromania and it didn't stun. Actually it felt like it didn't even do dmg. At first I thought maybe I miissed? But now I'm perfectly sure that it sometimes stuns and sometimes it doesn't. I have a theory that maybe it happens when you flash ult or protobelt ult, but I haven't tested it. Does anyone have the same issue? If you have maybe a playback of it maybe we could send it to riot to look into it.