I went through a nether portal and paused the game before the nether was able to load. When I unpaused nothing loaded other than mobs who were stuck spinning in place. I was able to walk and navigate the area as if the environment was there. Changing game mode did not fix the issue, but I was able to navigate as is normal for that mode (free roam on spectator, fly within the bounds of blocks on creative and walk on survival) as if all blocks were invisible but there. Saving and reloading did fix the issue.