This is an old bug that’s been around for a very long time. It’s not new and plenty of people who have worked with large levels have experienced it. If you never have then it’s only because you’ve never worked with large levels, that’s all there is too it. If you go to the marketplace and contact the guy’s from Real Biomes (They are basically one of the very best biome designers you’ll find on there) and you contact them, they will explain to you what I just did…that this is a bug…you can simply restart the engine/level and continue.
I enconuntered this problem several times. switch shift +1 , shift +2 ,shift+3 many times , then the problem is solved. 
2 Likes
Dude 4 years later and you are my hero.