Problem #1: No matter if you hit them, or are in creative mode post being in survival mode(And getting aagro of the mobs), the guardians will constantly have the "aggro beam" on you.

It will only let up if you get out of their sight, or let them despawn by some sort of other creature remover plugin.

Also, the amount of damage which it's doing seems a little bit larger than usual. With protection 8 unbreaking 8, etc. As described in the Environment, it still does 1- 1 1/2 hearts each tick, and doesn't let go. As far as I can remember, it used to stop it's beam after one hit, then reposition.