Well it might just be that the fabric is too thick. I am thinking that perhaps the needle isn't feeding into the bobbin properly (when it goes down below the bed) and so is not making a stitch. A blunt needle would mean you're not piercing the fabric enough to reach the bobbin properly, but likewise really thick fabric might be the issue.

Can you try going reaaaaally slowly, say using the hand wheel and see if you pick up the bobbin thread at all? How is if sewing on other parts of this garment? Or have you tried similar garments since this one?