I know that feeling pretty well. I'm not generally looking for a new position (although, readers should feel free to offer), but a job opened that seemed like a good fit at a place a good friend of mine works. It was somewhere I had previously interviewed when I was on the job market, so I thought it should go pretty smoothly.

As with your experience, it's not exactly that the interview went poorly, but it didn't go as well as most of my interviews had gone when I had to do lots of them. Oddly, my previous interview with them didn't feel great either, so maybe there's an element of it not being as good of a fit as it seemed.

A funny note about that interview is that my office ceiling light fixture chose that interview as its time to fall from the ceiling and shatter on the floor.