Falling blocks pop off before touching blocks around it

Could you explain how to replicate this.

The falling block will pop off if it isn't aligned well with the hole. You can use this command to see that everything works well:

/execute align xz positioned ~.5 ~ ~.5 run summon minecraft:falling_block ~ ~10 ~ {BlockState:{Name:"minecraft:sand"},Time:1}

I think you had the gamerule doEntityDrops set to false so it didn't drop.

I've resolved it as Invalid.