We are beginning to explore an issue where various Macs shut down instead of going to sleep, either when manually put to sleep by the user, or when automatically set to sleep via the Energy Saver pane of System Preferences.
In some cases, the issue can be resolved by deleting the following property list (.plist) files:
After deleting these files, restart and check for persistence of the issue.
Another workaround involves resetting the afflicted Mac's PMU (power management unit) can sometimes resolve this issue.
Instructions for resetting the PMU for various Mac models are contained in the following Knowledge Base articles:
A number of users also report that resetting NVRAM/PRAM resolves wake-from-sleep issues. In order to perform this process, shut down your Mac, then start it back up while immediately holding the following keys: Command, Option, P and R. Hold the keys down until the computer restarts and you hear the startup sound for the third time.
If you are experiencing a similar issue, please let us know.Resources