I had this thought... they've been taking our feedback and set it up in a specific sequence.

Many people suggested dungeon nm's could maybe be "fished up"... and 1.19 is largely about DoL tweaks.

What if the 5th chest was going to be implemented in the next patch, with an NM you must fish up in the area on the map marked "Guard House"? Only way I can see that room having any real purpose presently.