When an entity goes through a portal it can be clipped into solid hitbox entities such as boats and shulker boxes. It will however move the entity away from solid blocks that intersect the portal for example a glass block on two sides of a two wide portal. 

In order to recreate this bug:

First see normal behavior-

create a 2 wide portal on nether and overworld sides and send an entity through

See how entities behave when adding blocks-

add blocks bordering the lowest level of nether portals, then send an entity through to that side and the entity should be raised 1 block higher then before

See how entities behave when having solid hitbox entities inside the portal-

create a 2 wide portal on the overworld and nether side and put a boat with a passenger inside the portal on one side and send an entity through. You will see that the entity is put directly inside the boat instead of how it behaves from the previous test.

The expected behavior should be for the entity to be moved exactly how it is for regular blocks as it is for the solid hitbox entity. 

Just for anyone who wasn't aware entities move in there portal to try to avoid colliding with things as of 1.19.3.