I've always had morality with Adel (when making choices with her), except maybe towards the end (when you can go to the bathroom when she's there), and I had the option of penetrating her in the shower (i think the MC had low morality at this moment). She says no, she wants to give her virginity to the MC but not like that in the shower, and that's after that the MC can go to her room and finally have sex with her.
I think the bug/glitch comes from there.
Either we are not supposed to be able to do it (yet the scene and the dialogues of his first time are there), or we can do it but the trigger is missing to take the next step in terms of affection.