Just adding more.
The milkshakes with Misa quest seems to trigger every time you leave a school area. For example, going from first floor to second floor at school, second floor to first floor or leaving the school building etc etc but at ANY time, not just after school.
Not happening when leaving a classroom, though.
It switches to the characters outside, going to the milkshake shop and then ends back at the MC room with a black screen. Menu's work and you can interact with objects, but nothing is visible.
Can navigate out by just moving left and holding down, takes us outside and fixes the black screen. But once you go back to the academy, it triggers all over and repeats.
Editing this to add that it never progressed the quest. Worth noting this happened on a Friday. On Monday, talking to her in the morning at school causes her to get angry, and then she again asks to get milkshakes. The same bug occurs at this point, if you try to go upstairs or leave, it skips to the scene of them at the milkshake shop, she says it's too loud and they leave and it just black screens at MC's room. Can't progress it at all.