router suddenly reboot by watchdog

Hi
i have hpa lite router model RouterBOARD 941-2nD
After upgrading from 6.34 to latest OS (6.39.1) i have noticed that the router daily reboot itself
the log say router rebooted by watchdog without proper shutdown
the watchdog is active but no ping address chosen

What is the problem ?

Firmware current is 3.32
Please Advice
Thanks Forward
Ronen - 4Z4ZQ
http://www.ronen.org

Deactivate the watchdog.