Giants unhittable/invincible

No one in my server are able to hit giants for some reason. its not consistent and so far its only been moose/goose and dragonfly. They can still hit us but we cant hit them. the attack animation plays but the giant doesn't react to it, health not lowering and no stun affect. %95 sure its not a lag issue either, as we were able to hit the lava larvae with no issue or delay, and I could also hit the walls we set up just as easily so it doesnt seem to have to do with server lag. what usually happened is the fight started normally but after awhile the boss just became invincible. we DO use mods, but the only one that has to do with enemies is the combined status mod.