The portal animation can sometimes play after travelling through it. Usually happens in creative mode, but can also happen in survival.

Can be caused by MC-262358, but not exclusively.

I found another way to reproduce it, but it also isn't 100% consistent. It happened in survival mode. The player has a very brief cooldown between travelling through portals. If the player goes out and back into the portal very quickly after changing dimensions, it can cause this as well.

Steps to reproduce

1. Entering the portal
2. Walk in and out(Walk out distance about 0.587 block) of the portal immediately after loading the dimension.
3. Repeat the above steps until successful reproduction.