Mobs dont take damage on my private server is this a known bug or unique?

I tried to kill with my sword and my daggers the little shellbacks and the big ones and a croc none would die and did not appear to take damage they did get bloody but health bar never went down. I hit them seve5ral times after they were bloody as hell and they just wont die

Same thing happened after server and client restart

I have a 20 person server hosted by Host Havok

Thanks any help would be appreciated.