Invulnerable Bosses?

is it just me or do several of the pit bosses suddenly have the same glitch as Varshan where once they get a DR or shield or w/e it is it never goes away? I have had several fights recently where I am destroying the boss, taking it down to 5-10% in under 20 seconds and then taking 5 min or more to whittle down the last 5-10 %. it makes no sense what is going on? this seems to happen mainly with Blood Bishop and Mothers Judgement.

EDIT: it seems to have something to do with DOT damage. it seems like if they receive DOT while the shield is up then the shield does not stop until they stop taking damage. Is this intentional or should the shield time out at some point regardless of incoming damage? it doesn’t seem right and it wasn’t happening a few days ago.