I am on an Android Moto Z^2 Play phone.

When building nether portals, the first pair work as expected. But when you build a second nether portal in the overworld, it will link to the original portal in the nether from a much farther distance. I have personally tested it at over 500 blocks (the distance between the two overworld portals), and have heard rumors of well over a thousand blocks. You can still link up portals properly, just makes it much more difficult as you have to travel to the desired location on foot in the nether.

How to recreate this bug:

1. Build a standard nether portal (4×5 obsidian frame, although I'm sure you know that XD)
2. Go through the portal and stay in the nether waiting for the player cool down for going through portals. (Not essential but I recommend placing a non-nether block as a marker for that portal ie. Cobblestone or clay)
3. Go back through the portal you just came out of, you should come out of your original portal.
4. Go roughly 500 blocks away from your original overworld portal (as I said I have heard it rumored much farther so you don't have to be overly finicky with it)
5. You should see that you appear in you original portal in the nether.