Thanks everyone for your input. I've considered everything that I understood. Someone thought I was using blue bobbin thread. What you are seeing is the blue washable marker that I used as a guideline for my feather stem. There are no number adjustments on the HQ 16, and it is a sit-down model where I move the fabric. The quilt isn't on rollers.
I took the bobbin case to the HQ rep at the show this morning. She found that I must have dropped my bobbin case at some point, and it was slightly out of round. She bent it back and adjusted the tension. She thinks it will work now. Hopefully, this will solve the problem, but I've ordered another bobbin case. Since my carpel tunnel surgery my hands are more clumsy, and sometimes the case drops to the tile floor when I'm changing it.
She also recommended taking out the bobbin genie that I was using when using Superior So Fine thread. It is thicker than what I usually use in the bobbin. She said the bobbin genie's are good for thin threads, like Isacord or DMC embroidery thread, but not for thicker threads.
The HQ rep also thinks taking off the paper ends of the prewounds would work better in my bobbin case.
I only use YLI monofilament thread in the top. I've quilted many quilts with it, and I prefer the look. I also don't have to worry about buying yet another thread spool in just the right color if I use the clear thread. It makes life more simple. Up until this quilt I have used DMC embroidery thread in the bobbin at the recommendation of Harriet Hargrave. The only reason I tried the prewound bobbins is that I heard that they would save time, and they hold much more thread so there would be fewer bobbin changes... eyes rolling... best laid plans and all that.
I have one more block to rip out, and then I'll try the bobbin that the HQ representative adjusted. Crossing all of my fingers and toes that this will work.
Pray for me y'all...