I am aware this question was noted for the RUT955, but also applies to RUT240 running firmware version 1.12
The router system-reboot logs show a periodic reboot triggered at 0200 every 7 days, even though periodic reboot is not enabled (ping reboot is enabled, and working correctly).
I suspect that if I enable, then disable periodic reboot, the problem will go away, but wanted to note this for fixing in future firmware releases.