Why is the slider getting jammed on invisible zip?
Check that there is sufficient clearance for the slider to pass along the length of the zip. Check that no side seams interrupt the travel of the slider along the chain. Check that the edge fo the coil is not stitched to the base tape of the zip.
Why does the garment bulge out at the side where the zip is inserted?
Check the tension of the sewing machine is not too high. Check that both the fabric and zip are fed evenly through the sewing machine. Check that the sewing machine feed is balanced. Check that the stitching is equal density on each side of the zip.
Why is the open end part of the zip found to be broken when returned by the end customer?
In long centre front applications the end of the zip can be placed under high strain. Check that the end consumer does not create too much pressure to the bottom end of the zip when wearing the garment. If the application is a long coat a two way zip maybe required.