Anivia ultimate going invisible (BUG)

As anivia main i remember the good old times of invisible q bug that i loved :P was sad when it was fixed, but now i get a new chance to relive the good old days... Jokes aside for the last 3 games i noticed that even tho my ultimate wasn't canceled it's animation and sound effect completely vanish under some conditions, tried testing if its just me or is it also for the enemy team, placed my ultimate in middle of the jungle in a place where i was sure they would pass trough sat in bush, after making it go invisible and just as expected they walked right trough it semi confused a bout the slow and the damage.

Don't know why but i wasn't able to recreate it in early late game, only in mid game, maybe just bad luck, however when fully charged or about to be just walk to the edge of its casting range and sometimes it just vanishes, replay didnt save so dont have any video, gonna try doing it again, if i get any footage of it ill leave it in the comments