If you summon a mob and a falling block riding it, after some time, the block will turn into an item and pop off of it.
In the attached video, a falling block was riding a baby zombie, and after some time, the block popped off.
MC-206755
Falling blocks pop off of other entities after some time
Resolved
Invalid
0
Falling blocks drop after a certain amount of time (
TimeNBT tag).