Steps to reproduce the bug:

1- Place a repeating command block near you with this command in it:

kill @e[type=minecraft:falling_block]

2- Set the command block to "Always active"

3- Place any gravity affected blocks (GAB) (sand, gravel, etc ...) in a case where the block is supposed to fall

4- The block won't fall until the command block is deactivated AND the GAB is updated

Demonstration video: https://youtu.be/k8AQ_MDccMY

The only command blocks used on this map are those shown in the video, and there are no custom datapacks loaded