Creation of new nether portal after one has already been used

I have had a hardcore world for a few weeks now, and have had a nether portal set up since the first few days. Today, 8-11-20, the release of 1.16.2, after going through the portal from the overworld to the nether, and then back to the overworld, the game created a new nether portal about 300 blocks away from my original portal.