Lower render distances cause mobs to be deleted when teleported a long ways away. For example:

1) Create a superflat creative world
2) Set your render distance to 5
3) /summon Pig ~ ~ ~

4) /tp @e[name=Test] ~ ~ ~1000
5) /tp ~ ~ ~1000
6) The pig got deleted and there is no sign of him
7) Set your render distance to 16 and rinse and repeat the commands and observe that the pig is alive this time.

May relate to https://bugs.mojang.com/browse/MC-98210 ? Also this doesn't just effect pigs, it also effects things like AreaEffectClouds.