Nether portals that are linked will occasionally delink and create a new portal.
Eg: 7, 7 in the nether connects to 0, 0 in the overworld, and there are no other portals. It works fine 30 times in a row. Suddenly, when coming back to the overworld, a new portal is created at 56, 56. When you go back in and come back out, it takes you to 0, 0 as normal. But now occasionally It'll take you to 56, 56. If you break the portal at 56, 56, you will consistently go to 0, 0, until one day, it generates one near 56, 56 again.
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Is the behavior dependent on where you enter the portal from? If so, please provide precise details.
Can you please provide the world seed and if possible, a copy of the world?
What device(s) are you experiencing this on?
This ticket has been temporarily closed as Awaiting Response. It will automatically reopen when you add information. Tickets that do not contain enough information may be closed as Incomplete.

Is the behavior dependent on where you enter the portal from? If so, please provide precise details.
Can you please provide the world seed and if possible, a copy of the world?
What device(s) are you experiencing this on?
This ticket has been temporarily closed as Awaiting Response. It will automatically reopen when you add information. Tickets that do not contain enough information may be closed as Incomplete.

Tested on multiple windows 10 laptops, mobile, and xbox.
Experienced in multiple different worlds.
The coordinates provided were example coordinates. It occurs regardless of nether portal positioning. No matter what the coordinates, world, or device, nether portals will occasionally delink from their originally connected one and instead generate a brand new one at game-determined coordinates (just as it would if the original portal is broken, except that it is not broken, it is intact and should be treated as such by the game.)

Please see the linked ticket for a brief explanation of portal linking.

Please see the linked ticket for a brief explanation of portal linking.

Please see the linked ticket for a brief explanation of portal linking.

Thank you for your report!
We're tracking this issue in MCPE-39609, so this ticket is being resolved and linked as a duplicate.
That ticket has already been resolved as working as intended, which means this is not considered a bug and won't be fixed. Please do not leave a comment on the linked ticket.
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Thank you for your report!
We're tracking this issue in MCPE-39609, so this ticket is being resolved and linked as a duplicate.
That ticket has already been resolved as working as intended, which means this is not considered a bug and won't be fixed. Please do not leave a comment on the linked ticket.
If you haven't already, you might like to make use of the search feature to see if the issue has already been mentioned.
Quick Links:
📓 Bug Tracker Guidelines – 💬 Community Support – 📧 Mojang Support
📓 Project Summary – ✍️ Feedback and Suggestions – 📖 Game Wiki
-- I am a bot. This action was performed automatically! Please report any issues on Discord or Reddit

Thank you for your report!
We're tracking this issue in MCPE-39609, so this ticket is being resolved and linked as a duplicate.
That ticket has already been resolved as working as intended, which means this is not considered a bug and won't be fixed. Please do not leave a comment on the linked ticket.
If you haven't already, you might like to make use of the search feature to see if the issue has already been mentioned.
Quick Links:
📓 Bug Tracker Guidelines – 💬 Community Support – 📧 Mojang Support
📓 Project Summary – ✍️ Feedback and Suggestions – 📖 Game Wiki
-- I am a bot. This action was performed automatically! Please report any issues on Discord or Reddit

This is not the issue.
I would understand if it, instead of going to the 'wrong' coordinates (0,0) created the portal at the 'right' coordinates (56, 56) and consistently went there. But that is not how this is working.
When the portal at 56, 56 is created, it does not link there permanently. In fact, most times, it still takes you to 0, 0, the wrong coordinates. But occasionally, it will take you to 56, 56. (or any other coordinates, 56, 56 is just an example).
That is the inconsistency that I am reporting: it does not send the player to the "new portal as close as possible to the calculated coordinates".
I'd also like to note that the information provided in MCPE-39609 is contradicted by the world NBT data: portals do actually have a set 'list' of 'target portal coordinates' that they're linked with, if you open the world up in MCCToolchest or UME, you will see this. Presumably, the issue is that the NBT data is either incorrectly overwritten, wrongly prioritized, or incorrectly called.

We would need a specific set of steps (and possibly a copy of the world) so that the issue can be replicated. Having only general examples is not enough to show that this is a separate issue from MCPE-39609. If you think this is indeed a different issue, please clarify using this format:
Steps to Reproduce:
1. (be complete and precise so someone else can repeat your exact steps)
2.
3.
Observed Results:
(briefly describe what actually happens, including exactly where you exit the portal)
Expected Results:
(briefly describe what should happen)
(attach video to help explain the issue)
Attach or link a copy of the world.

We would need a specific set of steps (and possibly a copy of the world) so that the issue can be replicated. Having only general examples is not enough to show that this is a separate issue from MCPE-39609. If you think this is indeed a different issue, please clarify using this format:
Steps to Reproduce:
1. (be complete and precise so someone else can repeat your exact steps)
2.
3.
Observed Results:
(briefly describe what actually happens, including exactly where you exit the portal)
Expected Results:
(briefly describe what should happen)
(attach video to help explain the issue)
Attach or link a copy of the world.

We would need a specific set of steps (and possibly a copy of the world) so that the issue can be replicated. Having only general examples is not enough to show that this is a separate issue from MCPE-39609. If you think this is indeed a different issue, please clarify using this format:
Steps to Reproduce:
1. (be complete and precise so someone else can repeat your exact steps)
2.
3.
Observed Results:
(briefly describe what actually happens, including exactly where you exit the portal)
Expected Results:
(briefly describe what should happen)
(attach video to help explain the issue)
Attach or link a copy of the world.

Steps to Reproduce:
1. Create a nether portal in the overworld
2. Create a nether portal in the nether at coordinates (Overworld/8), as one does when making a nether portal
3. Enter the nether portal repeatedly
Observed Results:
A 2nd nether portal will be generated in the overworld, quite nearby to the portal created in step 1. When entering Overworld Portal #2, you will still arrive at the Nether-Side Portal. When entering the Nether Portal, you will come out at Overworld Portal #1 (as created in step #1), but occasionally you will come out at the 2nd nether portal.
Expected Results:
By the nether portal coordinate system, the Nether-Side Nether Portal should remain linked to Overworld Portal #1, because the coordinates are correct (divided by 8). It should not generate a 2nd Overworld Portal
Overworld Portal 1 and the nether portal should be consistently linked, without randomly, occasionally generating (or linking) to a 2nd Overworld portal.
Is the behavior dependent on where you enter the portal from? If so, please provide precise details.
Can you please provide the world seed and if possible, a copy of the world?
What device(s) are you experiencing this on?
This ticket has been temporarily closed as Awaiting Response. It will automatically reopen when you add information. Tickets that do not contain enough information may be closed as Incomplete.