Arduplane 4.0.9 froze in the middle of flight

pbarker@bluebottle:~/rc/ardupilot(pr/decode-watchdog-fix)$ ./Tools/scripts/decode_watchdog.py "WDOG {TimeUS : 29876615, Tsk : -3, IE : 2048, IEC : 1, IEL : 218, MvMsg : 0, MvCmd : 0, SmLn : 0, FL : 122, FT : 3, FA : 136073120, FP : 59, ICSR : 4196355, LR : 135416151, TN : stor}"
    T            Scheduler Task:           -3: Waiting for sample
   IE       Internal Error Mask:         2048: ?????
  IEC      Internal Error Count:            1: 1
  IEL       Internal Error Line:          218: 218
   MM           MAVLink Message:            0: [None]
   MC           MAVLink Command:            0: [None]
   SL            Semaphore Line:            0: Not waiting on semaphore
   FL                Fault Line:          122: ?????
   FT                Fault Type:            3: HardFault
   FA             Fault Address:    0x81c4fa0: ?????
  FTP     Fault Thread Priority:           59: ?????
FICSR        Fault ICS Register:    0x4196355: [Below]
         VECTACTIVE:   3  (Hard fault)
          RESERVED1:   0 
           RETOBASE:   1  (no (or no more) active exceptions)
        VECTPENDING:   0  (Thread mode)
          RESERVED2:   0 
         ISRPENDING:   1  (Interrupt pending)
          RESERVED3:   0 
          PENDSTCLR:   0  (WO clears SysTick exception)
          PENDSTSET:   0  (SysTick not pending)
          PENDSVCLR:   0  (WO clears pendsv exception)
          PENDSVSET:   0  (SysTick not pending)
          RESERVED4:   0 
         NMIPENDSET:   0  (NMI not pending)
          FLR Fault Long Return Address:    0x8124957: ?????
   TN               Thread name:         stor: ?????
pbarker@bluebottle:~/rc/ardupilot(pr/decode-watchdog-fix)$