Unknown system crash

Asterisk 13.4.0

Been running perfectly for several weeks now, and as luck would have it, I take a day off and the system takes a dump.
Not sure exactly what happened, but apparently it started acting like the were no trunks. Anyone trying to call out couldn’t and anyone calling in got a message that the number they were calling could not be dialed. A reboot fixed it, but I’m concerned that there may be a underlying problem somewhere. And I really don’t know where to start. From the log it looks like it all started at 16:30 yesterday. Any ideas where I should start ?? Thanks