Vacuum in tank + rising outside pressure = fuel backflow?
When I read about the cavitation evidence in the fuel pumps, I immediately wondered if maybe a vacuum had built up in the fuel tanks, for example because the vent valve (used to let air enter the tanks as needed) might have been stuck.
A vacuum in the fuel tanks, combined with rising outside ambient pressure (plane approaching sea level), might ultimately lead to air bubbling backwards from the engine through the pumps and into the tanks - or not?
Two factors may have precipitated this condition exactly during the landing approach: The first factor being the ever increasing outside air pressure; and the second factor being that the engines were temporarily put into idle, presumably also reducing the pressure in the fuel supply pumps, which then would be more vulnerable to air flowing backwards than they were during cruise.
Once air starts flowing backwards through the pumps, they probably would not recover for quite a while.