Thread revived as the NTSB final report is out: a rare simultaneous dual-engine malfunction.

Probable cause, pasted from the report:

Corrosion of both engines’ variable geometry (VG) system components, which led to their operation in an off-schedule position and resulted in near-simultaneous sub-idle rotating compressor stalls on approach, subsequent loss of thrust in both engines, and an off-airport landing. Contributing to the accident was inadequate fault isolation guidance from the engine manufacturer, which prevented the identification of corrosion buildup in VG system components during troubleshooting of hung start events of both engines about 1 month before the accident.