Benedict VS bosses and certain mobs issue?

When i fight some bosses especially ones with key hit spots i always get “immune” come up instead of a damage indicator or nothing comes up even when i use my boomsday ill see immune come up

this is also the same for the ice golems im hitting them in the hit spot but “immune” comes up alot.

and also on the bosses when i do moves like boomsday on them it will show no activity or immune on their health bar that i lowered their health