This happens when the looper or hook fail to enter the thread loop during the stitch formation. Possible causes are
  • Incorrect timing of the looper or hook
  • Incorrect setting of the take up or pull off devices
  • Needle vibration or staggering
  • Wrong size needle hole plate
  • Needle deflection by resistance of the material
  • Loss of thread control due to the wrong size needle being used for the thread used in sewing.

Lock stitch skipping
Chain stitch skipping