Adding an additional user to split screen hangs

When adding a new user to split screen after Minecraft has been running for a while, Minecraft hangs while generating terrain for the second user.

 

Steps to reproduce

1. Launch Minecraft using a local realm, with multiplayer turned off
2. Play for a while.
3. Let your system go into rest mode
4. Have another player press the ≡ button twice to log in

Results:

The screen is split, and the loading screen is shown for the second user.  The loading screen displays "Generating Terrain", but the progress bar never fills up at all.