We’ve narrowed it down to the possible mis-matching polarity between the top connections that are on the roof of the sauna and the interior corner connections. You will need to remove the (large) dust cover on top with a phillips screwdriver and inspect the red and white connectors on each side (blue connectors for the mid/large saunas also).
See if it's loose or a cable is not connected. We believe that during transit and the fact that we twist the cables that it may not be fully connected. Please push the connections downwards from the top.