The top thread is NOT catching the bottom thread while sewing.

generally it is a needle thread tension problem so increase the tension right up
it could be a needle /hook timing issue if you had had broken needles lately

Tension for stitching a quilt sandwich is tricky. It helps if you use the same color for top and bobbin thread,. If your quilting thread is not the same weight (either heavier or lighter) than thread used for regular sewing, then the bobbin tension may need to be adjusted. My quilting thread is lighter weight so I have a separate bobbin case whos tension has been adjusted specifically for quilting. The goal is have both threads meet in the middle of the sandwich. If the top thread is showing under the sandwich, you probably need to tighten the top tension so it will pull the bobbin thread up into the sandwich. Do the reverse if the bobbin thread shows on top.

It may also make a difference by changing the type and size needle. I tend to prefer a top-stitch needle. An embroidery or microtex may also work for you.

Machine Quilting Thread and Tension

Tension troubles on your quilting machine Try these tricks

5 Free Motion Quilting Problems and How to Fix Them

Quilting is a bit more finicky than regular sewing. Be sure to ALWAYS RAISE the presser foot when threading the top thread. FWIW, I use a separate bobbin case for FMQ that I have tightened the tension to keep the bobbin thread from coming to the top of the sandwich, but I tend to use a finer thread for quilting so adjusting the bobbin takes care of it. In your case, however, it sounds like the top thread is staying under the fabric. I would try tightening the top tension. Also, install a brand new needle--a top stitch, embroidery, or microtex needle seem to work well for me. Test well on a sandwich made of the same fabric and batting and get it adjusted well before sewing on your quilt. Sometimes sewing speed will affect stitches under the fabric, or even on top.

5 Free Motion Quilting Problems and How to Fix Them

Correcting Sewing Machine Tension for Free Motion Quilting NQC

LOOPS Tension or Speed

https://www.generations-quilt-patterns.com/machine-quilting-thread.html

https://www.generations-quilt-patterns.com/sewing-machine-tension.html

https://www.generations-quilt-patterns.com/machine-quilting-tension-problems.html

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Is the top thread making a thread mess under the fabric? That usually means the top tension is too loose or the thread is not seated in the tension disk.

Remove the top thread from the machine.
ALWAYS RAISE the presser foot and rethread from the beginning.
Set the top tension at the midpoint and test your machine. Then adjust the tension until the two threads meet in the middle of the fabric.

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Ashleigh--Your machine will work satisfactorily ONLY if the presser foot is down. When the presser foot is up, the tension disk is released, therefore, no tension = a big knot of thread.

To free motion quilt, you should drop the feed dogs. Install a darning foot (this foot is shorter in length so when it is lowered, there is a space between the presser foot and needle plate). The space allows the fabric to be moved easily while stitching.

Some sewists will free motion quilt without a presser foot (if they don't have a darning foot), but that is very dangerous as one can easily sew through a finger. However, even when sewing without a presser foot, the presser foot mechanism needs to be lowered in order to properly form stitches.

How to Free Motion Quilt on Regular Sewing Machine

try using a longer needle, or lowering the one you have now by loosening the needle screw and dropping the needle down some

It sounds like one of your clearances in the machine is off. When a machine skips stitches like yours is doing, it does so because the hook responsible for "catching" the thread from the needle is not close enough to the needle so it misses the loop of thread from the needle. If your machine was having a timing problem it wouldn't sew well on any fabric. A clearance problem shows up on certain fabrics at certain times. A few things you could do to try to compensate it would be to use a slightly larger needle and turn your top tension dial down to a lower setting. Move the machine a little slower on the frame or increase the speed of the machine. Either way a trip to your technician will be needed. Make sure you tell him to check the needle to hook clearance.

If the thread is shredding and breaking, there is an incompatibility of your needle, thread, and fabric. Could be old, bargain bin, or poor quality thread--does the thread have little "hairs" of thread lint sticking out of it--that's probably not good quality. Look for fresh, good quality thread. Try a brand new needle--a sharp if you are sewing woven fabric. Make sure the thread is not too big for the needle eye. Sometimes, a top-stitch needle or embroidery needle will work well on FMQ. (A top-stitch needle has a longer scarf which helps protect the thread during the multiple times the needle penetrates the fabric before the thread forms a stitch. Shredding means the thread is getting worn out before it forms a stitch. A piece of thread penetrates the fabric 10-20 times before it forms a stitch.) Could also be a snag somewhere that is damaging the thread.

Sewing Needle Troubleshooting Guide

SCHMETZ Household Needle Chart

Most FMQ instructions say the upper and bobbin tension should be the same, however, I find my machine works a bit better when the bobbin thread is just a little tighter than the upper thread. Then the bobbin thread does not "pop" up on the top of my fabric quite as much. It's probably something you will just need to experiment with in getting used to your machine.

P.S.--when threading your machine, make sure the Presser Foot is ALWAYS RAISED so the top thread will seat properly in the tension disk. Failure to do this will cause thread barfs (usually referred to as thread nests or bird nests) under your fabric. Also, before beginning your FMQ, ALWAYS PULL the bobbin thread to the top of the fabric, then hold both thread tails gently in your left hand while you slowly take the first couple of stitches.

How and Why to Bring up the Bobbin Thread

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Try a different needle. Use a quilting or topstitch or even a metallic needle - one that has a larger scarf than normal. The scarf is the groove at the back of the needle where the thread goes while the stitch is being formed. Quilting threads often need more "room" there. I have been told that the Inspira quilting needles are good because they have a thread groove on the front and the back of the needle. Not tried them personally but might be worthwhile for you to consider.

For the looping, you could fiddle with your tensions a little either loosening the bobbin tension or tightening the top, or both. Only ever do this in very small increments. But the good news is that even the "professional" quilters do not have perfect quilt backs - just have a look at them at quilt shows!
Pam M.

Might be that you need to lower the tensions quite a bit, you'll have to juggle with top and bottom tensions though, and experiment for just this operation with the Sensormatic.