Traveling through an overworld nether portal does not create a corresponding nether-side portal

Following reset of nether in an existing world (Seed -1932358799), and loading the world into Beta, traveling through existing overworld portals at [2569, 77, -217] and [2438, 65 35] do not generate corresponding nether-side portals, and place the player inside netherrack. The world was initally generated in 1.15.