Invulnerable Mob

Had an issue yesterday in waterways (Act 3 Normal) where i had an invulnerable critter on me, i could not target it but it could still attack and deal damage to.

https://imgur.com/a/N2PEgoX

it followed me throught the whole map.
https://imgur.com/a/jU2TwX5

and is probably still there (quit for the night after the map...)