Synology got back to me and said that my issue has a fix identified that will be released in DSM v6.1 bundle. The current baseline is DSM v6.0.2, and v6.1 is a beta version that is available. Since I’m trying to stabilize this system, I did not want to run a beta version of the DSM operating system. Instead Synology provided me an updated Intel firmware version M.616.
Installing the firmware seemed to help, the system installed the firmware and then rebooted without my needing to manually power cycle the system. Manual reboot and shutdown also worked. This time the system firmware also appears to have been updated:
Fingers crossed now! Hopefully this will be the end of the power management issues. The next test will be when there is an update to the DSM software and if the system can reboot after updating DSM.