Entities sent through a gateway can be invisible to players who are either already on the other side of a gateway, or are being sent until that player rejoins.

Steps to Reproduce:

Multiplayer:

1. Have two players join a multiplayer server
2. Put one at the main island, and one at the tp location of a gateway
   (can artificially create one if needed)
3. Have player at the main island send an armor stand through the gateway

Single-player:

1. In the end main island, recreate this setup on any gateway:
   
2. Force load the chunk(s) that the redstone is in

   /forceload add ~ ~
   

3. Press the button, and go through
4. Wait a few seconds, and look for the armor stand

Expected Result:

Multiplayer:
The player already on the other side of the gateway will not see the armor stand until they rejoin.
Single:
You will not see the armor stand after traveling through until you relog.

Observed Behavior:

The armor stand would be teleported through the gateway, and properly display to all players without needing to rejoin.

Screenshots/Videos:

ArmorStandEnd.mp4
After rejoining: