When I a used drawbead in the forming analysis, it was observed that some of the elements which moved over the bead line were distorted, and there is no obvious reason for this effect. What might be the problem?

I do not know what is the exact source of this problem. However, I was very lucky with several similar cases. I simply put a load curve to define the normal force for the drawbead, and the force defined in this curve can be very small (up to 10e-05). It works perfectly.