If an entity is teleported as soon as it's summoned, it will look like it's in the same place but actually be where it was teleported to.

Steps to Reproduce:
1.Place a repeat command block with the command:
/tp @e[tag=tag] ~ ~10 ~
2.Place a conditional chain command block next to it with:
/scoreboard players tag @e[tag=tag] remove tag
3.Run the command:
/summon Zombie ~3 ~ ~

4.The zombie will be summoned, fall below the ground, and then appear again after landing.