I was having the same issue, but I think I fixed it. Here is what I did, it would be cool if more people could play test it.
After my sim became a young adult (Saturday) the graduation event did not appear for Sunday. I waited the whole Sunday and nothing, but then on Monday I noticed there was an interaction my sim could do with other sims -> Highschool -> ask about graduation (can remember the exact wording but something like that) after clicking on it the graduation was added on the calendar for the following Sunday, it worked with no problems.
BUT, in case this is relevant for any EA dev out there, the plot thickens.
Because a week passed, at the point my sims could graduate, she had already moved out, married, and have a child. So, the husband attended the graduation. He was automatically added to the event on the calendar. That’s fine. The thing is, even affected graduating, they kept having the ask about graduating interaction, and at some point, it triggered another graduation event. Meaning that my sims graduated twice. Yet diplomas never came in the mail….. After the second graduation, the interaction was finally gone, and no graduation is showing. I don’t know if that was triggered by adding a second young adult to the household, but again, they both graduated twice.
Also, before doing this, I was experiencing the no-judge glitch for the sporting events (cheer and football, have not tried the other ones), but after it, I have the Finchwick fair event glitch. In any case, have not been able to properly play any after-school event. Not sure if all of these glitches are related somehow. In case this is relevant, I started playing on Henford-on-Bagley and then moved to coper dale. So, I don’t know if that triggers the afterschool activity glitch changing to another glitch or stating.
FYI I play with a ton of mods/CC but not MCC, this file is old and also has the not being able to climb mount Komurabi glitch and the prom working but not showing up in the calendar glitch.
General thoughts, did somebody actually play-test this thing before selling it?