dspy8083 About 20 times today the phone shuts down and restarts on it's own. Then, when I am using it, the phone shuts off, then reboots.
Unfortunately this description is consistent with a hardware failure. You might try taking it to a repair shop for an opinion.
Other options will be disruptive. If you are willing to wipe your user data, you could try running a "factory reset" by booting into Recovery. Or, if you can OEM-unlock the device, you could try flashing back to Google's stock OS.
Unfortunately it is not rare for problems with the flash storage to show up after an update, because a system update writes a lot of data all at once.