I have also witnessed sometimes that after updating my Galaxy j6 to One ui 2 the device automatically restarts sometimes but once I started optimising my phone using the device care on settings app and Samsung members app this issue is not there for me now.
We request you, kindly register your concern in Samsung Members app (Samsung Members app > Get help > Feedback > Error report) along with screenshots, short videos and error log file, so that we can assist you accordingly. Note: Please send device log files within 15 minutes of issue occurrence along with the exact issue details.
