The bug

When any non-player entity enters an End portal the obsidian platform is not regenerated. This can cause them to fall in the void if the obsidian platform was removed in the meantime.

What should happen:
Non-player entities (or at least pets?) should regenerate the obsidian platform in the End dimension.

How to reproduce (multiple players)

1. Have a player enter the End dimension and destroy the obsidian platform. Keep that player loading the area.
2. Have a second player push its pet into the overworld End portal.
   It will fall into the void and die if there are no blocks under the spawning point.

How to reproduce (single player)

1. Place an End portal in the overworld at a known position

   /setblock 0 5 0 end_portal
   

2. Make sure the portal is loaded (/setworldspawn or /forceload)
3. Enter the End
4. Remove the obsidian platform
5. Summon a wolf in the overworld above the portal

   /execute in minecraft:overworld run summon wolf 0 6 0
   

   The wolf is teleported to the End, but does not generate the obsidian platform