So you have a lots of things to do. Well, it is interesting about some bugs during gamedev. Like you say, some enemies, you hit them and they dont recieve damaga..whileother enemies are allright. Interesting case.
Viewing post in Mystic Dungeon Update 1.01 comments
I personally haven't encountered this bug so I'm not sure what causes it for only certain enemies. My assumption is that the players that encountered the bug were on higher levels which caused enemies to not take damage from certain attack types due to their resistances/weaknesses.
It could've also been that the bug in the damage indicator lead them to believe that the enemies weren't taking damage when they actually were.