So when you try to go in a portal in creative while being pushed by a sand pusher, you are there client side but it serves side. After 25 seconds or so, you get teleported back to the nether portal and this time you are really there. The game will regenerate a portal if there's not an existing one. During the 25 seconds where you are bugged, you can interact with entities, but they don't see you as being where you are, they see you kind of inside the portal. They can inflict you damage, but you will only get it after the 25 seconds. I don't understand everything that's happening, and I would appreciate if anyone would help me. (Btw this is partially caused by the sand pusher, even though this time it wasn't active at all. It went back to normal after I relogged.) When there's no existing portal in the nether, it will teleport me in a location that seems to be corresponding to my overworld portal coordinates. It will not recreate a portal until it snaps me back after ≈ 25 seconds (which are actually random), where it will create the portal. Watch a demonstration : https://youtu.be/35oOw8GkL90