Steps to reproduce:
Create a new world (flat preferably)
Start breaking a block
While the block cracking, don't let it break and pause the game with ESC.
Save and Quit to Title and rejoin the same world.
???
The block cracks are still there, and the block's state is not restored even if you rejoin the world.
See attachments below for an example.
Confirmed in 1.16.1 and 20w28a. Related to MC-8472, MC-54587 and MC-69865. I would suggest forward-resolving MC-154673 to this ticket as this one has been kept more up-to-date and contains clear steps to reproduce.