Klondike,
I have experienced a similar situation with my Auber PID. When I start to pre-heat my DBS6 and it's reaaaaallllly cold outside, my PID will flat-line as you described. I have had to open the Bradley, grab the PID sensor, warm it up with my hand, and make sure that the Bradley continues to heat.
I think that the Auber is probably not designed to operate in hyper-cold temps. Both batches of summer sausage I've done in the past three weeks required me to "fool" the Auber into thinking that the temp in my Bradley was over 32 F. (The second batch I had to warm the sensor three times before the PID engaged, and did it's thing). Once I get the temp in the Bradly above 32F, everything seems to work just fine.
Jeff