Skips threading in between sewing.

Hey everyone!

So heres a good question. Does anyone know why a commercial grade juki sewing machine would be skipping stitches while sewing? I work at a location where this happens a lot and we have to outsource the labor for repairs. However it would be beneficial for the company to have someone there to fix this issue. Please let me know as far as what could be the issue and maybe how to go about this maybe? I do appreciate all of you guys and thank you for your help!

-Daveyloder