My sister kind of took my game from me, I only got to do chapters 1 and 2. Once she got to Chapter 9, I got really excited. I've seen a lot of people wondering if Ruvik's appearances are randomly generated. I'm thinking they are for one reason, but I am not sure, so I wanted to see where he's appeared for everyone. Don't think I need spoiler tags, but just to be on the safe side...
His second appearance was at the top of the library where you get the upper safe dial. He appeared before she even got off that area. In fact, he got her when she was going down the ladder, which killed her. I don't know if his touch knocked Sebastian off the ladder or he pushed Sebastian, I couldn't tell. She said push.
Here's why I'm thinking it's random: we were all geared up to run after grabbing the upper dial. No Ruvik. There were many Haunted around, wondering maybe if it's random or if he's programmed not to be around so many Haunted. (By so many I mean like five. I know, sooo many.)
He then appeared in Ruvik's Room after picking up the file.
We didn't see him again until he appeared about two rooms down after she activated the final brain off his parents' room. He either chased her to the entrance hall or appeared there again, I can't remember. I'll have to ask her when she gets home.