I've been able to attend graduation ceremonies with two of my sims. Graduation is shown in the household calendar but not in advance, only on the Sunday it takes place: Shortly before 6 pm there is a pop up: If you agree to go to the event, you can choose some of your household members to go with you. I'm sorry that a lot…
Have you used the report option in the EA app? There's a thread about this issue in AHQ: https://answers.ea.com/t5/Technical-Issues-PC/Current-Issue-Book-Nook-Grunge-Revival-Show-Unowned-After/m-p/12619949#M252970