I've been using a Pilot Metropolitan pen with an F nib and a screw pump converter cartridge which was included with the pen for quite a while, and for all this time it has been intermittently stopping to flow ink properly.
It's definitely not a case of ink drying because it usually happens during long writing sessions, and fixes itself immediately if I turn the screw to push out some ink. My gut feeling is that it's either air bubbles get into the flow somehow, or, conversely, the air pocket I leave inside the converter is way too small and creates a vacuum when some of the ink flows out.
I have used other pens in the past, most with F-adjacent nibs and don't recall this happening on any of them except this particular one.
What can I do to prevent this?