Using the command /summon to create a falling sand entity, with or without extra data (for what it should become when it lands) does not work properly. The entity is created, but instantly disappears.
Linked issues
is duplicated by 2
Comments 4
Sand entities require a Time value greater than 0, otherwise they will despawn. To get a falling sand entity to fall properly, the command should look like this:
/summon FallingSand x y z {Time:1,...}
Confirmed.