What causes hairiness in threads?

Check working condition and parts of sewing machines (i.e. hook, bobbin case, throat plate, needle tip, sharp thread guide) plus thread quality and material thickness.

I have untwisted thread, why is this and how can I prevent it?

How do I minimise skipped stitching issue on quilting machines?

Multi-needle quilting machine is running with fabric lifting process in a multidirectional. Putting higher lubrication level on sewing thread will help minimise the issue. Tensions should be also adjusted correctly.