Why are the zip teeth being damaged during washing?
Ensure an M46 or M60 zip is being used. Ensure zip slider is closed during washing and ensure the button is fastened where ever possible. If button is not present protect the zip from the stresses of the washing process. Ensure no overloading of the washing is occurring.
Why does the neck opening bulge out at the bottom 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 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.