My $8 amazon "circuit analyzer" arrived and I have the same reversed polarity issue as you. When connecting the 767 to the wall you hear a loud click internal to the unit then the polarity of all 4 of the 20-amp sockets are reversed. Pull the plug, hear a click, and the polarity is restored. I don't have the correct adapter to test the 30-amp socket, maybe I'll look up how to use my volt meter to run this test.
Regardless of the result of my easy start RV air conditioner install it looks like I will be returning this particular Anker 767. I will await delivery of my easy start before initiating the return as that will inform me whether to even bother getting another 767.
IMO this reverse polarity issue is a complete deal breaker for anyone thinking of using the 767 as a UPS.