Always prepared spells are gone

My player's paladin: https://www.dndbeyond.com/characters/159826415

All his oath spells are gone from his spell list.

This is a bug that occurs when a 5e Paladin subclass is used with the 5.5e Paladin class. It's been there since the release of the 5.5e core books almost two years ago, but they haven't done anything about it yet.

Some people have had luck with creating homebrew copies of 5e Paladin subclasses for the 5.5e class and using those instead.

Is it possible the player unchecked 5e Core Rules in the Character Settings?

no its checked on