I apologize for my multiple posts on this thread, but I am following up on the issue on my HTC One M8 GPe. Since I disabled the Lookout SIM Theft Alert yesterday, the daily reboot occurred right on schedule again today, captured in the Reboot Logger app at 1903, but Lookout didn't generate any Threat Alerts. Unless you have the Reboot Logger app installed, it's very easy for spontaneous reboots to slip by unnoticed, especially if you don't use a Security PIN or Password. In my case, I use a PIN, but with Trusted Places (Home) and Trusted Devices (my Pebble Watch) in the Smart Lock feature, so I usually don't have to enter my pin unless I leave home, separate the watch from the phone, or if the phone reboots, and in each incidence that Reboot Logger has captured, the PIN entry was required of me, and in a couple of instances, I had tried to use the phone while it was in the process of crashing and was non-responsive, and I forced a power recycle trying to get a response from the phone. Other than that, the reboots have been completely spontaneous.
FWIW, the only day this last week that the problem didn't occur, was on the day that we traveled about 50 miles from home to visit family members at the time it usually would have happened. I'm not sure yet what to conclude by that, but it might be quite relevant.
At this point, I really don't believe that Lookout is the underlying source of the reboots. If anyone else is sharing this problem, it would be very helpful for us to compare notes between us to help isolate the source of the problem. The only good news so far is that it is so predictable, and it seems I'm not alone in experiencing it.