Since 1.17 released nether portals have not been behaving as expected.

When traveling through existing portals, in either direction, the game fails to translate the coordinates when entering the opposite realm. For example, if I enter a portal at overworld coordinates 1600x800 I arrive at Nether coordinates 1600x800. If I then go back to the overworld from Nether 200x100 I arrive at Overworld 200x100.

This happened to me twice in version 1.16, and has become very consistent since 1.17 released.