I made a nether portal in the overworld,(portalA) lit it up and then created a copy of the same world on creative, to first check the nether spawn for any potential dangers. I spawned in a small cave (in the nether) (portalB) near a lava ocean and went back through the same portal. i ended up on a mountain approximately 100 blocks away (portalC). I then broke the portal. (I know this happens if the portal in the nether cannot be placed at the ideal coordinates.) Then I went to the nether on my survival world. I went through the exact same nether portal (portalA) and was expecting to come out in the same cave. Instead, the loading screen for the nether (netherrack background) just changed to loading screen for overworld (dirt background). When I came out, I was in an overworld cave (portalD), approximately 100 blocks away, not in the same location as on the creative world.
I think that going through the same nether portals on two identical copies of the same world should result in exiting through the same portal as well.
While I was getting coordinates of portals for this bug report, another problem occured to me. I was trying to get coordinates of the nether side portal (portalB) on creative, so I went through. I stepped out of the portal, everything looked normal and after a few seconds, I was placed back in to the portal, like I was stepping out again. (I have previously experienced being placed back into the portal and exiting again and thought it happened because of lag) Then it teleported me back to the overworld (portalA). The same thing happened, when I tried again. When I went through for the third time nothing unusual happened. (maybe because I waited in the portal for a second before stepping out) Going back to the overworld, everything went fine. This time I went back through the original portal (portalA).
seed: 1883875724119310463
coordinates:
original portal in the overworld: 150 66 36 (A)
nether side portal on creative: 3 24 7 (B)
exit portal on creative: 15 136 56 (C)
exit portal on survival: 15 95 -33 (D)
Comments


Is it still an issue in 1.20+? Did the workaround provided in the comment helped you with the problem, or it did not have any fix either?

Cleaning up old tickets: This ticket had been set to 'Awaiting Response', but has not received a response from the reporter (~3 months+) so is being closed as Incomplete. If you feel this is still a valid issue then please comment, or create a new ticket following the Issue Guidelines which includes steps to reproduce the problem.
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I was experiencing this issue, but solved it in my survival world:
When I tried to go to the nether, I took damage. Initially I thought this was suffocation damage. I'd go into the portal, take damage for a while, then appear in the overworld again. However, on one attempt, I actually got killed by a monster. At first I thought I went into the portal, took damage, then came out in the overworld (at some random location) and got killed by a monster there, but it occurred to me that the "suffocation damage" might just be a monster in the nether attacking me, and the reason I reappeared in the overworld might be because of collision with the monster or something. So I put Thorns enchantment on my armor and went in again, heard the zombie taking damage from Thorns, and then I appeared in the nether and could finish him off.
Through all of this I also saw symptoms of MCPE-159900: when I couldn't go through my regular overworld portal, I constructed another one 500 blocks east of the first one in my industrial district. When I tried to go through it I was killed by the zombie, but I found most of my dropped items outside my regular overworld portal. I had traveled to the nether, but to the same portal on the nether side that the original portal is linked to, got killed by the zombie there, and my items traveled back to the first portal in my industrial district. I will provide more details of my experience on that ticket.
I experienced this issue on v1.19.50 on Android.