Here is a breakdown of the bug
Once every third patch, a bug is added to Mei. This time it was not the wall (which they pretty much break every patch), but rather a bug where Mei cant headshot frozen targets was brought back into the game. Once targets are frozen their hitboxes go out of sync. If you shoot them in the head while frozen, it will in many cases not be registered as a headshot, but rather a regular body shot. The hitbox for the head is not where it should be.
As we all know, after the countless nerfs to Mei over the past years, it has become more and more of a headache to play her. Now imagen this scenario where you pop all your defenses just to stay alive long enough freeze someone. You’ve spent almost all your ammo, but have just enough to finish them off with a headshot. You hit them straight in the face, but the headshot doesn’t register and you are left with no ammo and most likely about to die.
I can’t even express how infuriating this is. It’s basically a death sentence every time this bug occurs.
TLDR:
Don’t use primary, stick to playing knockoff McCree with secondary.