Can confirm in Windows 10 1.19.50 for Shulkers. Replicated the bug on a fresh Creative world. In my testing, executing /setworldspawn in the Overworld "fixes" the issue; Shulkers sent through the End fountain afterwards will appear at the appropriate Y-level (this "fix" persists after relogging and works for sending a Shulker through when the world spawn is already occupied by another Shulker).
Can confirm in Windows 10 1.19.50 for Shulkers. Replicated the bug on a fresh Creative world. In my testing, executing /setworldspawn in the Overworld "fixes" the issue; Shulkers sent through the End fountain afterwards will appear at the appropriate Y-level (this "fix" persists after relogging and works for sending a Shulker through when the world spawn is already occupied by another Shulker).