I'm not sure this will help solve the issue, but... Have you tried loosening the top tension a bit for zz stitching? (5 to 4, 4 to 3). Generally, that needs to happen, whether zz ing with cams or built in stitches. It could be with the extra width traveled, the top thread isn't loose enough for the needle penetration with thread to catch the bobbin thread.
Following to read others' recommendations, and learn of your success.