Levels seem to "reset" when traveling across worlds (eg. overworld to end). The levels don't actually completely reset, but seem to become stagnant and in return, doesn't display a level, thus not allowing you to re-use the waystone until you obtain another orb to have the levels re-appear again.

Fixed 👍

This is a vanilla bug actually. https://bugs.mojang.com/browse/MC-124177

A temporary solution I done for lose of potion effects due to the bug is this. Not sure how one can fix it for xp tho
https://github.com/TelepathicGrunt/Bumblezone-Fabric/blob/a07d9912f766b1fbac7433539481ce18afade56c/src/main/java/net/telepathicgrunt/bumblezone/entities/PlayerTeleportation.java#L72-L89