Talking about this quest in Nonmoa Lake:
While doing this quest, the monsters will go randomly "Invulnerability" and regen all the health. This happened many times as I was ascending the poles. I guess the height differences in some areas are too great, resulting in this. I had to run away to "reset" the mobs.
After the quest I tried to ascend the poles for the vista. Same thing. So this looks like either a map bug or a height-differences bug. (Sometimes when you try to hit a mob from way up top, the game make the mob go "Invulnerable" to prevent abuse. e.g. c+1 spam at some location all day=free experience.)