Nether crash on reloaded save

Everything seems to work fine when initially creating a world (I can enter and exit the nether normally) but after quitting to main menu from the overworld and reloading, entering the nether crashes with a NPE at "Ticking player". If I exit to main menu while in the nether, loading the save crashes with a NPE at "Ticking memory connection". Both crash reports attached and the errors are consistent.