My world was created in version 1.11 and we created a long range nether travel network.

I will explain whats going wrong using a small asci graphic.
The graphic shows the locations of my 4 Portals (Letters A,B,C and D) in overworld and nether.

OW-Pos		0, 0		0, 1024		0, 2048
		|		|		|
		|		|		|
Overworld	A		|		D
-------------------------------------------------
Nether		X	      B | C		Z
		|		|		|
		|		|		|
Nether-Pos	0, 0		0, 128		0, 256

Travel Route 1	A<------------B   C<------------D
Travel Route 2	A------------>B   C------------>D

Before version 1.16.2 it was possible to enter portal A at location 0, 0 in overworld and arrive in Portal B at 125, 0 in the nether.
Because portal B is still within the 128 blocks range arround the nether location of portal A.

From there you should be able to enter portal C at location 0, 130 in the nether.
Basicly Portal C should connect to portal D at 0,2048 in the overworld, but before 1.16.2 there
was another bug MC-149705 that broke this part of the route (I dont talk here about this bug now).

If you walk enter portal D in Overworld it worked that you arrive at portal C in the Nether too.
So BEFORE 1.16.2 the half of the route worked from both directions.

The portals worked like that in each release version until 1.16.1.

But since 1.16.2 the route from A to B and the Route from D to C broke too.
Suddenly portal A and D no longer discover that there are existing portals in the nether, which they should be connected to.

Instead of this, new and useless portals X and Z are created in the nether at random locations

• around 0, 0 when entering portal A
• around 0, 256 when entering portal D

I know that this would be the correct behavior if Portal B and C would not exist or disabled.
But while portal B is in the range of 128 nether blocks, it should be connected to Portal A.
And while portal D is in the range of 128 nether blocks, it should be connected to Portal C.

I tried multiple times to destroy the useless portals X and Z, but everytime new portals are created around the same location.
And the minecraft world is very big, without long range nether travel it would be a pain to travel through the world to a far away place.

In total that means. if that bug will not be fixed,

ALL LONG RANGE NETHER TRAVEL ROUTES ARE DESTROYED.

I think that happened while they tried to fix bug MC-149705.
Because before the portal detection range was to low, when returning from nether to overworld.
It seems that instead of increasing the overworld portal detection range, exidently the nether portal detection range was reduced.