As I have been playing this game I have ran into these alote here is a pic . Be careful of them you well fall off the land.
As i see you use mods, so this may be this.
Look at the upper side of your screeen, like a skyrim compass, i know that’s a mod. It may be any outdated mod, or one not working with current testlive build simpy.
I would try start a new game without any mods, and see what this area around the mounds would look then. 
Ya .
Ya, what Vattende said.
Even if it isn’t the case that a mod is causing issues, testlive bug reports should never be filled if you are using any mods of any kind.