Hey so this actually isn’t a bug, this feature has been temporarily disabled in an attempt to fix another gamebreaking bug.
https://twitter.com/MarkYetter/status/1182117524533436416?s=20
Basically it’s a visual bug to do with her passive that prevents her health bar from updating and causes her to keep the username of said champion she had previously disguised as. There are many ways to trigger this bug, but one of the easiest ways of triggering it involved her ability to cancel her own disguise so they had to temporarily disable it.
Watch this videos for reference:
https://m.youtube.com/watch?v=9zDc3llGFjc
And here is a clip of this bug in game:
https://clips.twitch.tv/CallousSpeedyGrouseNotLikeThis
(This clip is not mine and is just an example I found on /r/neekomains, all credit goes to the streamer)
Ever been called a cheater/hacker or bug abuser playing Neeko in the latest patch? Now you know why. This bug has still been shown to occurr though even after they disabled this part of her passive. Neeko is my favourite champion and Is my most played champion over 3 different accounts and I have to say that with such a gamebreaking bug it’s very disappointing to see that riot hasn’t disabled her yet. It’s not that rare for this bug to trigger as It has happened to the enemy team THREE TIMES when I played Neeko this patch and I have also been on the receiving end of this bug in one game. Don’t worry though, we will get the undisguise button back, it may however take a few patches depending on how quickly they fix the bug unfortunately.