When creating a nether portal in 1.13, I've found that there is a high chance that it does not take the player to the correct over world location of 8 times the coordinates in the nether. Instead, I have been taken to the same over world coordinates as the coordinates in the nether. For example, if I create a nether portal at X 100, Z 100, I have been taken to the over world coordinates of X 100, Z 100 instead of X 800, Z 800. This has also happened where it does not create a nether portal in the overworld, leaving me stranded with no way of getting back into the nether. This has only happened with newly created portals.