check a few possible solutions, including verifying that the machine can still stitch buttonholes correctly and perform other advanced stitching techniques. If tension problems still exist, there may be an electronic issue with the machine
If you notice loose stitches or loops forming underneath your fabric, your first step should be to rethread the bobbin thread
To address this issue, the first thing you should check is the tension of the upper thread. Start with a tension setting of around 3-4 and work up one step if necessary.