Hmm did Ari ask you to be his girlfriend (cafe event) before Jon confessed or not. It could be a bug, it also could be timing, since Jon still can confess even though Katy dated but she shold not be able to accept Jon's confession, just be thankful of it or said okay. If you continue to romance both Jon's ending would probably pop out because he has a higher priority in the code, I'll check the code out and make sure if it's a system bug or a mistake on the coding. Thank you for reporting this, so sorry for your inconvenience!!