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That problem (known as 'birds-nesting' under the fabric) is typically caused by an incorrect tension setting.
There are of course two tension settings, for the two threads: upper thread tension, and bobbin thread or lower thread tension.
Birds-nesting below the fabric/work, means that the upper thread tension is too loose. Try setting the upper thread tension dial one or two points (at most, at a time) higher.
Then try a bit and see if it improves - or is cured. If it improves, but isn't cured, set it another point higher, try again, until it is perfect, then you can continue work properly.
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