Yes, I'm always 100% on the date, love is also at 70 and I've also received the invitation to join the band. I've had 15 dates with her now, but it just won't finish, even if I start a new game.
Weird, I just recheck this specific event and it triggers correctly.
Do you think you can join our discord server, create a ticket in #create-ticket and attach a save file and a little description to reproduce your issue?