I had my interview on October 25th, and I was given a "Decision can't be made" result even though an officer started my interview with going through I-751. There were no issues either, just them needing more time to review all my paperwork. It's very annoying but unfortunately it's common and the wait time differs depending on your local office and even depending on an officer. My status changed to approved/oath scheduled a week later. At the same time, I know a few other folks who passed I-751 + N-400 interviews at my local office, and they waited for 2,5 weeks and 4 weeks till status change. I think you'll hear from them within a month.