Thx for the feedback, it is very helpful! That fight is pretty hard to balance because of the weakness and strength of the monster (Same problem like before i guess). We had a playtest group wo nuked the chest and killed him pretty fast and one were they fought him in complete darkness, all their attacks had disadvantage and one of them even died.
Personally I like the strength/weakness of the monsters but maybe it is better to get away from this type of design. Not sure, it is hard to balance but players love it when they find the weakness.
But thx for the Feedback, i will keep it in mind <3 really appreciate it