If you have a long/high enough wall, then some of the chunks behind it don't show. They are still loaded because entities still move, but the chunks are still see-through.

The way I replicated it:
1) create new world
2) Use seed: 6992403603823021898
3) Go to roughly x = -314 z = 112
4) Run the command /fill -314 114 112 -357 64 112 minecraft:stone_bricks
5) Fly at some height above the wall and go forward and backward across in the z direction (y = 128 gets it for me)