Chunks render, but act as if the chunk isn't loaded.

Their is a world loading error where the player falls into the ground passing through blocks as if they were a ghost, NoClipping through the ground, until they hit the Void.
The rate at which they fall is about the speed of one falling in an unloaded chunk.
If trying to recreate this, you may have to relog several time for the error doesn't happen all the time.