Upon entering the world the overworld appears fine, however after entering and exiting the Nether after any duration of time the world fails to render a large section of the map. If I reload the world everyone has normal and proper rendering of the map until they enter and exit the nether again. This causes blocks in the non-rendering area to be invisible but still able to be interacted with, and allows us to see directly into caves; both discovered and not depending on the distance. Though we have tried to avoid exploiting this in any way, after we exit the nether we have to avoid this location due to not knowing where holes are. Any blocks in the area seem to be affected, even player-placed ones; my friends home for example.