In the pictured example opening 1 chest does not reveal the other chests, 2nd chest reveals chests, 3rd chest reveals map. Number of fights stays correct.
#Dungeon chests number reducing at 9 clears instead of 10
abstract veldt
elder canyon
I think there is a very small chance a chest spawns in the entrance or something, thus giving you one less chest?
so it has nothing to do with the clears and it's just... something that rarely happens
abstract veldt
Ok, I've noticed this 3 times on my 10 runs in various dungeons though