The bug

Falling block entities which are below Y -63 drop already after 100 ticks instead of the default 600.

Expected behavior

Falling block entities should drop as item after 100 ticks if they are below Y -64 because Y -63 can still be considered "in the world".

How to reproduce

Summon a falling block entity below Y -63 but above or at Y -64 with a Time value of 100

/summon falling_block ~ -63.1 ~ {Time:100,NoGravity:1b}

→ You will see that the falling block instantly drops as item