That sounds like mesh protection. If you fall (or intentionally climb or glitch) into or inside of the mesh, there is a system that will insta-kill you. There is a “soft spot” in the jungle, in a cave that is under a tree that will also kill you if you aren’t careful.

It sounds like you found a spot where you managed to work through the terrain surface.

Best to get the coords, and some screenshots, and report it to Funcom as a bug so that they can MAYBE get their world builder folks to patch up the terrain in those spots.