Check the following points or issues.

• The thread is not passed through the bobbin winding thread guide correctly.

  Correctly pass the thread through the bobbin winding thread guide.

  

  For details, see "How do I wind the bobbin?".
   

• Bobbin spins slowly.

  Press key in the bobbin winding window to increase the bobbin winding speed.

  For details, see "How do I wind the bobbin?".
   

• The thread that was pulled out was not wound onto the bobbin correctly.

  Wind the thread that was pulled off around the bobbin 5 or 6 times clockwise.

  

  For details, see "How do I wind the bobbin?".