If the machine sew fine on regular sewing then it can be a number of things. The thread is not catching the bobbin thread because.....you are moving the fabric too quickly, there is some resistance in the fabric surface (batiks), the needle is dull or not inserted correctly and is not piercing the fabric quick enough, the spool thread path is hung up on something, and last but not least, the timing could be off on your machine(repair shop)
There are other cause but that's all I can think of right now.