Steps to Reproduce:

Open a world and ask one of your friends to join in. After you put on a leather suit(with Thorns III), ask them to grab a Sharpness V Netherite Sword.(That will be able to kill you instantly with Critical Attack.) Then ask them to kill you.

Observed Result:

You're killed instantly, and they never gets any damage back.

Expected Result:

You're killed and they should get some damage in return.