Whenever any command like /home or /back is used to teleport across dimensions, your xp bar seems to be set to 0 until you gain xp again, at which point it resets to normal

This is a Vanilla bug, I'll have to look into how to fix this at a later date.

https://modrinth.com/mod/FabricCrossDimTPFix here is a mod that fixes this issue. Can be installed server side only