Originally Posted by WizardOfAZ
Duh. I had not inspected closely enough. One of the step screws had backed out from the vibration (photo below) and was preventing completely stowing on the left side. Tightened up, all good now.
Sorry to bother.
Screws loosening up will continue and need to be checked periodically unless you use some sort of light thread locker. There are also special washers and spring washers that are in the mix. The parts are almost all proprietary as well as pricey, like everything else Airstream. You definitely do not want the step dropping down and hitting something or $$$$$$.