My goal was to move a shulker, which was in a boat, through a nether portal, while being in the Nether dimension.

When I broke the boat with the shulker inside of it, positioned next to the portal, the boat disappeared and the shulker disappeared. I then came through the portal to find the shulker which wasn't there and finally located it with the help of a /data command to find that the shulker had been teleported in the overworld to its corresponding nether coordinates instead of multiplying the x and z coordinates by the expected factor of 8.