When you are moving the material the thread is 'flexing' away from the bobbin hook and that is why it won't pick up the thread. Try a larger sized needle, you may have less problems with a size 18. Also, move your hands slower and speed up the machine. That way when you move the sandwich the needle isn't in the fabric when you move the sandwich. The bottom line is that the timing is slightly off and really needs to be checked. Good luck!