Please put a detailed description in the bug tracker, I think you are referring to this reddit post: https://www.reddit.com/r/feedthebeast/comments/bb05fg/is_there_any_way_to_remove_this_square_im_using/

I do not have such squares, do you have another mod that could cause this? Optifine, Shaders?

I get this too but only with shaders which would make sense

Same as #113 , Try to using the newest Forge and Optifine, I'm using the latest version of Optifine and found no visual problems...