I want to summon a FallingSand,
but it doesn't show up when falling.

What I expected to happen was...:
I'm summoned nether portal,
end portal and end gateway,
they should be seen while falling.

What actually happened was...:
Only nether portal showed up when falling,
but end portal and gateway doesn't,
it only appears when it touches the ground and
become a block

Steps to Reproduce:
1.I summoned falling nether portal by
/summon FallingSand ~ ~3 ~

{Time:1,Block:minecraft:portal}

2.I summoned falling end portal by
/summon FallingSand ~ ~3 ~

{Time:1,Block:minecraft:end_portal}

3.I summoned falling end gateway by
/summon FallingSand ~ ~3 ~

{Time:1,Block:minecraft:end_gateway}

4.By Observation, only Nether portal showed up while falling.

In addition, other blocks might have the same issue, but
I got no time to test them all.