This has also happened to me. Sometimes there are "burrs" on the thread, but that doesn't happen often.

having the same issues in the pass but, these tips work for me.
1-schmetz HLx5 90/14 if using a juki or mid arm machine...90/14 top stitch for home machine...

2-low you thread little by little until you reach 2.0 but, check you back and make sure that the stitches are not loose....

these two tips have always worked for me... good luck

I had the same problem quilting a panel top onto a minkee backing and finally figured out to loosen the tension and lengthen the stitching. Finally it stopped breaking off! I was so relieved to figure out how to solve the problem. I needed to get the top quilted for my daughter before she has the baby in the next few weeks! Turned out fairly well, overall.

When my thread started breaking there were three reasons. 1)I found out it was a bad spool of thread. I was using Superior Rainbow and when I called them they sent me a new spool. There are 2 other reasons my thread snapped. 2) the machine needed cleaning because of lint build up in the top of the machine. 3) the thread was hanging and I bought a behind the machine spool holder.

You leave the feed dogs up, and set the stitch length to zero (0). The stitch length is what tells the feed dogs how fast/slow to move...setting the stitch length to zero, sets the feed dogs at just about nothing, if not nothing.

Another thing is to use a darning/embroidery type foot (not your regular foot).
I have done some quilting on my Singer 2662 (basic machine)...and it also worked better with the feed dogs up.

I have the same problems. Sometimes it's the batting it doesn't like, sometimes it's the thread, sometimes the needle. If I put a metallic needle in it usually works. Also my machine likes me to go slow when FMQ. Mine does not do well with polester batting and sheets as a backing. Just keep changing things until it works.

The very same thing kept happening to me! I was sooo frustrated. I actually ended up taking my machine back to where I got it and asked them for help. Turns out that my machine...I like to call her "Daisy Mae".....only likes certain needles. Anytime I use a needle she doesn't like....she breaks the thread!!!! I'd try changing needles til your machine is happy.

You need to use a metallic needle, then your thread will not break.

Are you using invisible thread in the top? If not, what?
Does your spool stand upright or lay down?
If it is lying down, do you have the property size thread cap on?

It can be any number of things ... that's just some things I can think of off the top of my head.

Spray basting isn't the cause. I've been quilting for about 8 years and have only used spray basting, never pins and it has never created a problem for me.