Hello, good to the developers of this good mod and well, as the name said, it is a chunk glitch that happens to me in some parts of the world in the experimental settings, which I think is the large caves option, which some appear with chunks. empty, here I show images and the Minecraft version:

My minecraft version is 1.12.2
To deny it, activate the edges of the chunks so that they can see

is there someone?

is there someone?

large caves was discontinued in the mod so it's quite unlikely this will be solved unless it's a problem in modern versions too