What's been bugging me more about this mechanic is that it's SO HARD to find out the "mysterious reason" in-game :( like, I've been playing long enough that I've (tentatively) figured out that 30 points up/down is usually due to dating (this one I'm not as sure of) while 10 points down usually means bullying (this one is 100%), but even when I have girls with the "paranoid" character trait and max friendship/influence with 10+ idols NOBODY TELLS ME ANYTHING.  At least for bullying, there used to occasionally be incidents where you could find out organically (the shouting match incident is the one I most remember, where you can eventually arrange a counseling session and find out that x is bullying y), but that hasn't occurred for me since the story update.   Now I have to ask every possible suspect who they're friends with, which unlocks the basics of their whole relationship chart, then find out who has a  "bullies" tab and just move the culprit somewhere else, or else move the victim to a sister group and never figure out the culprit.  Relationships only get revealed if you gossip with certain girls, and the relationships change so often that it barely matters.  It's driving me insane!!