I'm guessing you never fought Puzzle bosses before.
The Hunter is one such boss also The Factory you cannot brute force those bosses. Being marked is a punishment actually since yes it take a turn however it make all the enemies attack and crit the marked target.
I Don't know what could be the cause of this.
But I once seen the Hunter with Haste.
I pretty much brute forced the factory, just get those pocket watches and a growth ray and then you can charm all three robots and even if they are very overcharged, they deal low damage while charmed and then you can just punch repeatedly the factory until it dies, reapplying charm and healing your heroes, the growth ray is so that a pocket watch carrier can actually deal correct damage to offset the factory healing.