I've seen this happen on DeArmond pickups before and this is what I found. If the coil being wound did not have a guided traverse control to layer the magnet wire evenly back and forth, the coil would flair or expand the ends of the bobbin. If the bobbin is expanded at the ends, it can cause the plastic wall inside the bobbin to crack allowing the fine magnet wire to become lodged in the crack that can cause the coil to stop working or to become intermittent. If the bobbin has fine cracks, moisture can penetrate inside the coil and cause ICPC or inner coil pole corrosion.
DeArmond bobbins that use the 1/4" diameter pole pieces with individual pole height adjustment should be wound with coil machine that has an automatic traverse control. The automatic traverse control allows for proper winding pitch and wall tolerances. If you are having problems with this type of coil, make sure to check the injection molded seam lines for fine cracks that could eventually make the pickup inoperative.