I'm wondering if the accessibility service has anything to do with these random shutdowns. I've never turned on ART, but with several xposed mods, tweaksbox, and some debloating, my phone seemed stable for the first few weeks I owned it. One day I had a random reboot. It didn't happen again for a week or so, and then it happened once more. A few days later I noticed one of my tasker scripts (which reroutes gmail notification sounds through the headset iff the headset is connected) wasn't working. I checked the tasker accessibility service and it had turned itself off. After re-enabling it, my random shutdowns soon returned.
Anyone care to try ART with all accessibility services uninstalled? This would include talkback.