I'm going with the idea that something is interrupting exposure rather than development. View camera bellows have been know to harbor dust, lint, etc, especially in the folds, which can block light while airborne near the film, but not on it.
How often do you remove the bellows, clean, or vacuum out the bellows, etc? Also, I've had this happen on dryer, windier days. I used to carry my camera flat in a case, then assemble when arriving at the shooting place. Once I changed the case to allow the camera to be assembled all the time, just opened to change the lens, or film holder, the dust frequency diminished.
You may not be doing all this, but it's just a thought. Also, if possible, after inserting film, cocking the lens, I wait a half a minute or so, if I can, to let the inside air settle before pulling the dark slide. I don't know if any of this will help, but if this is a recent problem, depending on your location, it could be dryer and breezier than it was a few months ago.