I have run into multiple chunk issues where chunks spawn disconnected with the terrain on the border between the Ettenmoors and the Coldfells, and between the Ettenmoors and the Misty Mountains. These strange chunks have sheer bertical walls on multiple sides, usually the side facing the other Regions.
This is very common in Minecraft when updating to a newer version (or in this case mod version). That being said, it should only occur near previously loaded chunks. That doesn't seem to be the case for this one though.
I honestly have no idea what's causing it. If it is a feature, then it's the worst feature in the history of features! It makes the terrain look hideous.
It is not a bug and is intentional, at least somewhat. There are specific lines of code that make the Ettenmoors borders this way, but in some areas, it doesn't turn out as nice as others unfortunately.