Shulker Bug

Hello, I’m having a problem with shulkers spawning over the build limit after being transported to the overworld. My friends made a railway to transport shulkers to the overworld to use it in a farm. After the shulker entered the end portal, we couldnt find it in the overworld. We repeated this multiple times and the same thing happened. We ended up making a copy of the world and using commands to find them and they were all above Y 500. Please fix this bug