Which AC unit is working fine?
Is your 2nd AC unit 100% independent from the converter and distribution panel and all original RV wiring? If so, have you had any issues with it? Assuming not. If that is the case, look towards the problem being on the circuits running on the original electrical system.
Low lights on the DC circuit indicates a problem with battery charging. Cycling 120VAC running through your converter/distribution panel would seem to point to your converter too. Have you confirmed if there is constant 120VAC entering the RV as someone posted to check and for a 120VAC protection unit to see if that was an issue? If that is a direct connection from your pedestal and you know there is good 120VAC from it , to me, your converter seems suspect. Although very strange you would be having issues with it on a 2012.