Mercy has a visual bug with her res animation that has been in the game for about 6 years now.
When the player’s ping is low (below 200) her hand snaps quickly back into place and looks a little odd. But if your ping is high (200+) it looks how I’d assume to be normal, with her hand slowly falling down and moving to her staff.
This video shows what I mean: https://www.youtube.com/watch?v=3Pj3KYqJwQk
Hopefully this can finally be fixed.