I'd bet its the scraps of paper and the post its. The nicer paper for fountain pens actually has some kind of finished surface, which prevents ink from bleeding much at all. For paper where ink bleeds a lot, the surface of the paper is becoming completely saturated to the point where your nib is scraping soft chunks of ink soaked paper up as you write. That's probably what does it. If some of the paper is waxy, that could also cause clogging.

Different inks might have better results on a wider variety of paper, but that's something you have to try until you get something that works. I generally always either keep a high quality notebook around or I just use felt tip pens and keep my fountain pen at home if good paper isn't available.

Black and Red makes a decent quality notebook that's a good amount cheaper than Rhodia, Leuchtturm, etc.

Also stay away from moleskin they are trendy garbage. Ink bleeds like crazy because the paper they fill them with is of incredibly poor quality.