I had had this every 15 minute rebooting issue since early Feb and its now early May. I took my S in and asked for a firmware update somewhat hopeful that it would fix the problem, although two earlier updates had not. The the SC did the update, 2018.18.2 but it didn't fix the rebooting. And since Feb when the rebooting first started this was the first time that I had taken the car in. When they saw it didn't fix the reboot, they didn't stop looking for the cause. They elevated the issue to Tesla Engineering. Two days later I got a call from a tech, and asked me to check and report. They had fixed the problem completely. No more issues.
During the call with the tech, he told me that Engineering had found some OS files that were not in the folder that they were supposed to be. My problem had started right after the update from 2017.50 to 2018.4. I'd had at least two more updates after 10.4 and before the May update to 2018.18.2 and the rebooting had continued for those 3 months.
Bottom line is an OTA did not fix the problem, which I guess means the files in the wrong folder problem did not just disappear when a new update was installed. It too Tesla Engineering to find and fix the problem. And they did it remotely while my car sat in my garage sometime 1 or 2 days after I had left the SC. That's pretty cool. They moved those files from the wrong place to the correct folder remotely 2,400 miles from the mothership. Its not the distance that impresses me, its the granularity of the operations they can perform remotely. (I did not have to take the car in for someone to connect a laptop to fix it.) Makes me wonder what else they can do remotely, huh?
I do appreciate that the SC folks believed me when I first described the problem. They took it in and confirmed it was doing the same rebooting I had told them. And they stayed with the problem until it was fixed. I was in the IT business for 30+ years. When an issue is elevated to a higher expertise or permission level, there is always the doubt that the "guys below that level" don't know what they are talking about. These folks stayed with the issue and solved the problem. I am grateful for the SC's and Engineering's support.