The maturbation scene happens when you spy on her changing in the bedroom. (Peeking through the door in the evening) It's a progression of that scene.The only scene I'm missing is with Michelle in her bedroom at night the Titjob and masturbation scene , all I get is mc fapping away to the sight of her halfnaked boobs
She'll start taking her clothes of, playing with her tits and then start masturbating
Try doing all Michelle's scenes a couple of times and then keep checking if the new scene triggers.
I think you first need to get the masturbation scene before the titfuck scene then happens when you go into her room later.
Again the titfuck is a progression of the MC jerking off to Michelle.