Basalt Basin (Cave, Lv: 60, Dernel Jungle: -557, 31, -460)

Currently I am trying to 100% all of the caves in the game. Following the new update, the quest book now shows locations for caves, discoveries, side quests, etc. Now, I have completed every single cave exploration except for this one, despite the numerous amount of time I've spent trying to figure it out.

I just don't know how to progress through the cave, it is a dead end, but I can see the name tag for the chest below. It is definitely there, I've even unlocked it by slaying the mobs. I pressed all the buttons in the cave, explored the surrounding area thoroughly but I cannot find it.

If anybody knows and can explain where to go or what to do, I will pay 20 le for useful info. Thanks.

 

The cave is unfinished as of now, and is therefore inaccessible