Do you have any mods?
Please explain the issue is in as much detail as possible:
When I take crusader class for Jaethal she doesn’t have any domain slots in her cleric’s spellbook. However when I take ordinary cleric class, she does have domain slots. I think it’s because I can’t select any domain for crusader (it should be predefined, Jaethal already has 1 domain as Inquisitor but selection of domain is empty) and cleric has 2 domains so I can select second domain for her in this case.