Okay, first, I'm glad you could fix the evidence issue, I'm pretty sure that's not a bug, but just a misunderstanding of the mechanic (not sure!)
Also! you have to leave before 6PM, leave the school around 4PM, you also have to hide until you get to the gate, so starting the cutscene won't be interrupted by her!
Yeah the first problem was kinda my own misdirection, so it wasn't a bug just the goal being a little unclear.
As for the final competitor, I had always left before 6pm I just can't leave after killing her (as I get a game over warning if I don't) as the button to go home again doesn't work. When I said even when it hits 6, I meant that time just keeps going and doesn't kick me back home or start an investigation. I can sit in the classroom to skip time but Sakura just stands there unable to move after. I'm not sure if i'm generally doing anything wrong?