I kind of don't know how to explain this but in river cave (318s 68w) there is a little cave that BIO can access using its hover. (Not sure if blitz can get up there though also using its hover) but it looks like a cool nesting spot for BIOs but then if you head farther back into the cave, you can see the bottom of the world/terrain. I am probably using the wrong words to describe it but its better if you just watch the video
(If you are going to fix this please don't remove the cave entirely its a cool spot to hang out in. Just maybe cut off the cave so you can't see the ground)