Affects Version/s: Minecraft 1.10.2, Minecraft 16w43a, Minecraft 16w44a, Minecraft 1.11, Minecraft 16w50a
Fix Version/s: Minecraft 1.11.1
Affects any version 1.10.2 and forward, in a Debug world. Not sure about 1.10.1, since that was the crashing one.
Doesn't matter in what version the world was created. Happens in any gamemode, Spectator included.
Just open the world, and the following is spammed in the Game Output:
Submitted in case this indicates a wider issue than just a debug-world thing.