id have to agree i deal with electircal wiring and repair 6 days a week 9-5 and a bad connection will and can cause symptoms like this in a flex way.
Bad connection = more circuit resistance which in turn = less current making it to the Flexwatt element which finally = less heat generated. if current drops, so will the thermal output of the flexwatt, in fact that's what dimmers do they do not limit voltage, only current (amperage)