Originally posted by Boy Weevil:

terrain depth in this game is a bit wonky...it is based on the depth of the original terrain you're digging. a few meters away the starting height of the terrain would have been lower to start with, hence you being able to dig to a lower overall depth.

So, there's no way for me to dig past this bump?

Thats ♥♥♥♥♥♥ dumb.

This is literally a flat world, why do that?! Have a damn 0 Y coordinate!......