You may wish to try a different weight of thread. The thread you're using is a good brand, but perhaps your machine isn't happy with that particular weight. My Bernina acts up when I use a heavier weight thread. Someone suggested to me that I use a top stitching needle . . . I'm going to try that and see if Berniece will sew nicer that way.

I agree with re-threading and cleaning. You might also want to put in a new needle and wind a new bobbin.

Help
 

Love how the board jumps in and offers such good suggestions!! And the other suggestion -- does your machine need a good professional service/cleaning/adjusting? I quilt A LOT and have my machine serviced about once a year. Sometimes there is lint or thread that gets into the machine works and it's beyond our reach. Good luck, it's terrible when you want to sew and the machine won't cooperate.

I've learned that when my machine is sewing perfectly to take a cell phone photo of all the settings I'm using, the thread, how it's threaded into the tension disks, on thru the needle. How the bobbin is wound, and how it sits in the bobbin holder etc. These are great to have for reference for when my machine gets angry and messes up.

Needing a good cleaning is the #1 reason a machine stops working. Start there. Clean both upper and lower areas of your machine. Be sure all the deep fuzz is out of the bobbin area. If a good cleaning and other suggestions on checking the threading of your machine, change your needle. A burr can cause your machine to act up too. If all else fails then check with your dealer.

Wait a minute! Failed to upload? If I had that machine, I'd give it about five seconds to give me a straight answer before I introduced it to my baseball bat.

Well that's a helpful response. 🤔
She's talking about the picture she's trying to post in this thread. It won't upload. Probably because the file size is too big.

I have had a Sapphire for over 20 years and finally replaced it last year....with a new Sapphire. what model is yours?

OOPS! My bad. Nothing like taking & running with it.

What are the issues with the stitches? What are you sewing? piecing or quilting?

If you are quilting, be sure there is no drag on the quilt sandwich which can cause issues.

My machine needs the pressure foot "up" when threading to hit the tension disks.

Check the setting on machine. Is the machine in FMQ instead of sewing?

Are the feed dogs "up" or "down" on your machine?

Do you have the correct bobbin in the machine? Inserted and seated into the bobbin case?

What foot is on the machine? Is it set correctly and snug on the machine?

Go through the manual and be sure any settings are correct on the machine.

I don't have your machine brand but these are some common issues. Good luck!