After a while, Rexipher stop being able to be hit by Zaibas (Krivis) area skill.
It appears that your character was a bit bugged and that the skills were cast on a different layer or some sort. Like how spells kinda get stuck on hills and the like. Not really sure what caused it, but if it persists after fighting him again, leave the zone and come back, that may fix it.
Oh, I managed to eventually kill it (dink-dink-dink mode) but I wanted to report the bug. Thanks for the suggestion anyway!
Must have taken a while doing like 68 damage a hit. xD
What can I say? I’m a patient person. 
Same problem here. Tryed relogging, starting all over again, but after ~30 sec it still is ignoring Zaibas, Cure and Heal (all ground skills). And I’m not patient enough to kill him with my 13 dmg auto attack 
Problem solved. Stat reset scroll > max Str > 50-70 dmg with auto attack > 15 min of pain and boss is dead! 
