Expedition- unkilable mobs

No. They´d still take dmg and die before the regen kicks in.
Even if they didnt die, you´d clearly see them taking dmg.

Thats not whats happening, based on your initial description

dunno then. i guess i'll just spec out of expedition on the atlas. no point in investing so much points if i cant do half the encounters

Iirc you can check all active remnant mods at the lower right corner. So maybe take a look there, if you encounter "unkillable" mobs, in order to figure out which of the mods breaks your neck.

Sure, just skilling that expeditions can't appear anymore would work, but that seems for me like avoiding the problem, in stead of understanding/solving it.

If he is impending doom he is 100% taking immune to curses boxes. I took one myself by accident and it took me a minute to figure out what happened.

Just dont take immune to curses boxes and expedition is ok.

i may have taken curse immune by accident. will double check from now on.