I thought this had been fixed but I'm guessing not?
My teens aged up to young adults on a Tuesday which I thought should give the game enough time to trigger the graduation for the Sunday directly afterwards. They both got their third trait and any character value traits they had earned. They both got the pop-up saying they had graduated with honours straight after aging and they also both got diplomas in the post a day or so after aging, so I was hopeful graduation would work (as a previous save I had aged up a teen in months ago didn't get any of the above).
However, 5 days later on the Sunday there was still no Graduation ceremony on the calendar, and no pop up came at 6pm asking if we wanted to travel to graduation. I took them to the Auditorium anyway where a graduation was sort of taking place with sims in gowns, but my sims could not change into gowns or participate in any graduation activities. Really disappointed as graduation never works for me and one of the sims is a high achiever so I wanted her to get her graduation photo.
The save is a couple of years old and used to have mods and CC but both were removed months ago and I play with all mods turned off (vanilla) at the moment.