#7 will be the one

Because after you try each step pay attention to your tension. Tension is critical in LA quilting.

I did have a 16/100 needle, so I tried that. It worked! I fine-tuned the tension, and it sews like a dream.

I also had a 14/90 with large eye, and it also worked great. Each required a slightly different tension adjustment.

I'm so glad I saw the video about adjusting the tension, using dark/light thread in the bobbin/needle. It's also very interesting to see how the tension changes as I change directions. Stitching at a pretty fast speed, I can see bobbin thread being pulled to the top when I'm moving in some directions but not others.

I discovered the REAL cause of my thread breaking and skipped stitches. One of the sensors for the stitch length regulator was making poor contact with the carriage wheel. When moving in one direction the sensor would not immediately turn, so there was a slight delay between moving the carriage and the stitches. That caused the extra stress on the needle. The thicker needle helped, but the final cure was adjusting the sensor to get good contact.

Thanks everyone for all of the other ideas. I believe it's important to get all of the factors mentioned correct. I quited a queen size quilt over the weekend, and I could tell when something was not adjusted correctly, such as the height of the take-up bar, the top/bottom layer tension, foot pressure, thread tension, etc.