Boss Fight Bug

When I fight bosses, the bosses always heal themselves and the additional saves are pushed back like in a knockback even though I don't have that and heal in the uber boss fight from 1/4 life up to 3/4 even in the simulacrum farm where I brought in 2 different simufarmers when I didn't get the last wave of bosses down and they said that in over 2000 simufarms they have never seen kosis or the other one heal themselves I don't know what the problem is, it only happens to me and not my mates