Yeah thats what I thought, bullets were just going through him like he wasn't there.

That he isnt moving at all should give you an idea why this happend ;)

It's probably latency from a player or the server.

You hit most of them.  This same situation has happened to me before and I've gathered that sometimes hit detection just decides to take a cigarette break.

I analyzed it frame by frame. I missed 2 shots. The rest either hit him or went through him.

you missed most of those.  I saw dirt puffs, not blood.

Bullet Proof (seriously just look at it)