My client has heat-caused dermatitis from NBE treatment, how is that possible?

Additional information: “Device was set at 100% power and client readjusted the plate herself as she was uncomfortable.”

The fact that the customer adjusted it a bit herself is the problem. 
She lifted a bit her body to adjust the plate. The little fraction of no contact created a spark.    
Always be very clear and strict that the receiver plate must be well fixed on the body so that there is always very good contact.  
It is important to understand that if one makes the receiver plate smaller in surface than the active probe the receiver plate becomes the active side + it is resistive instead of capacitive.  In other words, if one lifts the body and adjust the plate the receive plate might have in milliseconds a smaller contact surface than the active probe.

Secondly doing a massage with 100 % power (which is not equal to 100 % effect) is not a good option.   
Doing a massage I would recommend a 80 % adjustment.