The bug

Falling blocks disappear when falling in unloaded chunks.

How to reproduce

1. Create a customized superflat world in creative mode with the following preset:

   minecraft:bedrock,2*minecraft:air,minecraft:gravel;minecraft:plains;village
   

2. Update the floating block
3. Wait until the gravel in loaded chunks finish updating
4. Walk few chunks away from your spawnpoint
   → Notice how the gravel disappeared and you can see the bare bedrock