I thought Sanctum hits only affected resolve, not life??

any ideas why this took life rather than resolve?

Because Sanctum monsters also damage health, just to a lesser extent than they would if the Resolve mechanic weren't there.

Sanctum mobs are slow, so it's easier to recover from a hit then in maps. But yes, you need some tankiness to avoid one shots in Sanctums.

And Lycia 1st form does more (and a lot of it) "real" damage than resolve.

And Lycia 2nd form does only (and a lot lot of it) "real" damage.

My guess is this phenomenon occurred because the program deducts your life/ES first before deducting your resolve/aspiration, hence it appeared like it bugged because you died with all your resolve/aspiration still intact.

These guards probably do a combi of phys and elemental attacks. The keywords here are "elemental" and "attack". That elemental portion cannot be defended by anything other than just your life/ES if your character is evasion/block and spell suppression based. It's that ice guy that hits hard so maybe increasing max cold res is the way to go.

I'm okay with this league, but not sanctums specifically. I won't miss it.