I was very annoyed with my Pilot Custom 742 with FA nib, which skipped every other stroke, thus breaking up my flow of writing.
I tried using different inks, including Waterman Intense Black, on different types of paper, to no avail.
I kept pondering on the issue, since I had a Falcon in SM, which gave out a lot of ink too, but never skip with the same inks nor paper.
When it was time to refill both pens, it dawned on me that the converter might be the problem. So I swapped out the Con-70 from the Custom 742 and put on the Con-40 instead. Sure enough, the ink flow greatly improved. So now I have to keep my bottle of ink handy during calligraphy sessions, since I need to refill after filling one and half page of A4 paper.