I've been running a RB4011 for a while now and I'm suffering from spontaneous reboots. I've had 3 in 4 weeks. The log always shows "Topics: system, error, critical, Message: router was rebooted without proper shutdown".
The router itself isn't doing anything spectacular. Just some standard stuff like Wifi + guest Wifi, couple of VLANs, simple firewall rules and a bit of queueing. Board identifies itself as RB4011iGS+5HacQ2HnD, running version 6.46.4 (stable). Hardly any visible CPU load and lots of free memory. Haven't upgraded the Routerboard firmware yet (current firmware is 6.45.1, upgrade firmware 6.46.4).
I have enabled remote logging and I noticed that around the moment of the "crash", the time of the router seems to have changed abnormally. Just before the crash, last message sent had timestamp "04:01:32", right after the "crash"/reboot, the next message had timestamp "03:52:55".
Could NTP be a factor? I'm not using (S)NTP but the Cloud feature.
What is the best approach to fight this?