The bug

First of all, in 1.16.1 when an item teleports it lines up perfectly and ends up in the center of the portal block (as you can see in the video). It only keeps its one-dimensional momentum. However, in this newest snapshot they don't line up perfectly and they keep all of their momenta. It is not a problem for me, I can work with that. I can find a way to delete all randomness from items and line up them by myself but the real problem is portal sides. In 1.16.1 you can choose the side you want to send entities. However, in the newest snapshot, you can't change nether portal sides! 

You can easily see all of the problems in the videos which I added.