On that aspiration, the conditions need to be right. The mentor needs to be level 10 in the instrument and the mentee must be level 9 or below for you to get credit. Now one thing I have noticed is that if you start the mentoring with the mentee being at level 8 or 9 and the mentoring maxes their skill before the 3 hours are up, it will still count as long as you don't stop. So it sounds like you meet the basic conditions since you get the mentor option in the first place. So it may be something else going on.
There is an old issue with milestone counts for a number of milestones that would not increment even though you did what you needed to do. It was fixed a while ago but I still have it happen on occasion in my game with a sim I haven't played in a long time. The music one is one of them that was affected but there are others. So are you seeing any issues with milestones in other aspirations that involve some type of counting not completing or is it just this one?
Another thing that could be affecting it could be a mod so what system are you playing on and do you use mods? If you do, have you tried running the game without mods and seeing if it works.
You can also try to repair the game again. Sometimes that does help with problems like the one you're having.
Now there is a way to move on if nothing else works. You can cheat the milestone to complete it. Open the command window and turn testing cheats on and use this cheat: Aspirations.Complete_Current_Milestone. That should complete the milestone and the aspiration for you since it's the last milestone left. Of course, if you are on a console, then using it will disable achievements but that is up to you to decide what you do for that.
Hope this helps.
I've tried loads of different sims and my sims is level 10. I've repaired the game again but it didn't work. I'm on PC but I don't want to use cheats as I still want the aspirations 😔
Ok I can understand not wanting to use cheats. I don't like using them either for the most part unless something is not going as it ought to like a stuck milestone. I prefer to do them as was intended. But just so you know, there is no penalty to using one on PC or Mac like there is on the console versions of the game. The milestone will simply complete and in your case with it being the last milestone to complete, so will the aspiration. Your sim will get the reward trait just as if you completed the aspiration through game play. I've had to do it several times in my main save to deal with a similar thing in various aspirations and have seen no downside to doing it when I've had to.
Hope this helps.
@Rain-of-Dawn96 This looks like it will get moved to General Discussion if it is about gameplay only. But just to make sure, have you looked in the bug section to see if there is any reports of the issue? I found this, that needs input, that is, more players to add their experience of the issue:
https://answers.ea.com/t5/Bug-Reports/NEEDS-INPUT-V-Musical-Genius-Mentoring-in-Music-Not-Fulfilling/m-p/9283391
Here are the cheats sanctioned by EA, I got it when I asked an EA representative if cheating was safe to do in the game:
https://www.ea.com/games/the-sims/the-sims-4/pc/how-to-cheat
