When breaking a block or place a block in the hole on the last layer of a large platform, the game stucks seriously, i.e. takes long to load and causes a not responding, no matter what blocks make the platform.
Step to reproduce:
1.Create a superflat world, which is a void biome or just lava + bedrock layers.
2.Create a large enough platform at a certain height, e.g. y=120

/setblock ~ 120 ~ 50 ~ 120 ~50 minecraft:stone

3.Break a block in the middle of the platform
4.Replace a stone at the same place

Step 3 and step 4 all experience a serious game stuck (Not Responding).

Looks like if it is very empty under the platform, the same thing happens.