When you say known good source how did you test to ensure the source you were connecting to when the SP said reverse polarity was good? If its not doing it all the time I would very much suspect the connectors you are using or the source you are plugging into.
Jake my sidekick (yellow Lab) 10/04 - 05/20
2017 RAM 2500 CC 4X4 Cummins Diesel
2016 Flagstaff 26 FKWS
AF&AM & El Korah Shrine of Idaho