When building and entering a nether portal in my super flat world, nothing unusual happened in the nether, but when leaving the nether, parts of the overworld wouldn't load, and some chunks I couldn't enter. These unloaded chunks would be in strange formations, or when I looked in a direction, all chunks in that direction would disappear. Mobs in unloaded chunks twitched and teleported. When I reloaded the world, the chunks returned to normal but would become glitched when re-entering and leaving the nether. I tested on multiple worlds with no plugins or addons, and it only affected super flat worlds and not normal worlds. I am not sure if this is specific to my computer, because I have not seen it reported anywhere else.