We have a server running in linux that we created in 1.15.
When 1.16 arrived, we renamed the nether world file by adding a .backup, so that it would generate a new nether for us, which it did... However, when we go through our portals, it does not create new portals or link to portals we build there. Instead it uses the coordinates of the portals before the reset and teleports us to the middle of nowhere, where those portals used to be, with no way to return...

We do have a few datapacks, but it is unlikely that they are interfering with this...

Video of the issue:
YouTube Video

All portals shown in the nether in the video above are player buildt.