I was playing one for all, and Evelynn got picked for my team.
After we hit 6 I noticed that Evelynn's slashers disappeared the more you died, until mine were gone almost completely. This only happened while in stealth post 6, and didn't affect abilities.
The bug doesn't show while watching the replay.
I'm not entirely sure if death is what triggers it, but it seems the most probably cause (I fed like a dumbass and I noticed mine were the ones most gone). We also played vs Nocturne is that's of any help.