Crossfeed valves
The FAA "leak" says
• The fuel crossfeed valves were closed in flight according to the flight crew, but the switches were found in the open position and only one valve was open. In the days following the event, the flight crew has added additional details to their report. The crew now believes they opened the valves just prior to impact and the airplane lost power before both valves moved to the open position.
It sounds as if there was a common feed to both engines, and that something in the right tank interfered with the flow to both engines.