Nether portals don't link up in the nether, and will take you to different portals when going through.

This started happening once we updated the server to 1.16.2, didn't happen in any previous versions.

The only datapack on the server is anti enderman grief from Vanilla Tweaks.

How to replicate:

Create a portal in the overworld, and another within link range

Go through the first portal, then exit

Go through the second portal

The game creates a new portal in the nether despite the second overworld portal being within range of the first one, and if you go back through it, it'll take you to the second overworld portal.