This is just information for other hunters out there, as I think I've brought this to the dev's attention via support already. Maybe this will make more sense than my ticket though. Wasn't 100% sure where to pop this but here's the basics:
The two aforementioned mobs (and probably others) have an ability called Indomitable. When Son of Gigaroth uses it, I believe it gives 30 secs of immense evasion; he cannot be hit by anything. The ability is on a 5 minute recycle, so it doesn't make SoG immpossible, but you'll be healing a lot for those 30 seconds
According to the wikia, Indomitable used to give immunity to root debuffs, so I'm not sure if that in itself is a bug. However, when Valkor the Impaler buffs upon spawning and uses Indomitable, he seems to have the buff indefinitely. I have yet to successfully dispel it, even when using Multi-Cast 2, Perfect Spell and Expulse 2 or Dispel 5. The group doesn't typically last more than 3 minutes before throwing in the towel, but we spend those 3 minutes missing Valkor with everything.
Firstly, I challenge all hunters out there to dispel Indomitable! Maybe as Conj with the highest Multi-Cast, good luck
Secondly, I challenge the devs to fix it, pretty please
It's kinda the only thing I've done for the last 6 months and it's been fun! But there's lots of people who are trying to hunt for the Valkor weapon pieces, so whatever was change, if it could just be changed back super quick, that'd be totally awesome!
Thanks.
Happy hunting all, see yas in Istaria
iuvenilis