I thought resists were calculated clientside as well? afaik healthjumping exists because client and server couldn't agree on wether the mob hit you or not. Might be an object in the way serverside but infact, the barrel is far to the left thus the mob could hit you on your screen but server says there was a barrel in the way and your health jumps back, because we all know, server > you. This also explains why you can lose health behind objects and hills even if the mobs could in no way hit you clientside.