Describe the bug
When any entity travels through the end portal (inside the end), the expected functionality is for it to land somewhere within the spawn chunks.

Reproduce
Drop sand into the end->overworld portal of a superflat glass world

Expected behavior:
Drop sand in portal, sand falls ontop of the terrain given.

Actual behavior:
drop sand in portal, sand falls into void

Note: once the spawn chunks are loaded, this is no longer a problem, so with larger chunks of sand this does not appear to be an issue

Versions
ServerCore: 1.2.5 - 1.18
Minecraft: 1.18

This is pretty severe as it lead to my server losing the dragon egg, and some of their horses when coming home victorious from the end.

Behavior is the same with servercore 1.2.4 - 1.18

Did you try downloading the "new" 1.2.5-1.18 version?
I updated it to fix #7 , which is pretty likely to be the same issue.

I downloaded the new mod versions day of writing this issue.

Commit 47fbe54 should resolve this issue, and many potential others regarding respawning, end portals, etc.