Hello, everyone!
I have a suspicion that Hrothgar's Chill set is working incorrectly (not according to tooltips) since Update 32.
Actually, I couldn't get it procced from any of my (i.e. Warden's) stun or immobilization abilities, except Dawnbreaker of Smiting and after i block an incoming channeling attack (sadly, by the time I write this post, I could test it on mobs only). Abilities that stun (such as Dizzying Swing) don't proc it even when I stun targets with Hrothgar's Chill set fifth effect active (prior to Update 32 you just had to damage a stunned enemy while your fifth Hrothgar's Chill effect was active to proc it; a source of stun could be from backbar weapon etc.) I thought, maybe my weapon enchantment somehow affects Hrothgar proc because of the Update 32 proc changes, but it seems that this is not the case.
Update 32 notes on Hrothgar's Chill state:
Hrothgar:
Fixed an issue where this set could proc off other sets that applied Stuns or Immobilizes.
Fixed an issue where this set was not following its listed proc requirements and applying in situations it should not have been.
But its tooltip states that it should proc from any stun or immobilization (maybe not from the damage after a stun or immobilization, but surely from a stun or immobilization ability other than Dawnbreaker of Smiting!). I think, either Hrothgar or its tooltip should be fixed.