I"m going with poltergeists. They always mess me up

Glad the problem is solved, even if there is no answer for 'why'.

It's not ghosts, it is gremlins.

I have an HQ 16. When I first got it, it skipped stitches. It was so frustrating. I finally figured it out. I wasn't pulling the thread back and forth in the tension disks to get the thread to settle all the way into the disks. Can't say that is or was your problem, but you may want to try that. Also lint and dull needles can cause a tension problem as well as incorrectly inserting the needle. Good luck (that old needle will not work forever, so I hope your problem can be solved).

I used to think it was the way I held my mouth, or if I had the wrong shirt on, maybe a full moon. Sometimes it just doesn't make sense.

Sometimes you just get a bad needle or package of needles.

I think Gay might be onto something. Machines clearly vibrate when we sew, even the smoothest ones. It doesn't take much for something to get just enough out of line to cause problems.

I'd say it was the lint. My viking hates lint. When it starts acting up I clean out the bobbin area and all is well.

Any chance it's the type of needle? You didn't mention if you were using a microtex, topstitching, quilting or universal. Also, what fabric are you stitching - batik, traditional quilting cotton?