Every instance in any area around 400 blocks away from spawn, I have tried to build nether portals and activate them, only to be met with a pool of lava and instant death. I have checked Chunkbase ( my world seed is -8578782874118800955 ) and I have checked most of the "estimated nether portals" surrounding up to 600 blocks from my spawn point to no avail.
I have built a nether portal around X: 72 Z: -424 where there is a Taiga village with a single villager, and that too is met with lava.
Based on the numbers you’ve given, all of the portals you have made are taking you to the same portal in the nether. In order to generate a new portal in the nether you need to create your overworld portal at least 1024 blocks from the first one you created, and possibly as much as 2048 blocks away. See MCPE-39609 for details.