External 27” Thunderbolt monitor sleep not working.

[MiamiC70]

After working properly for years now my external monitor a 27” thunderbolt connected to my MacBook Air is not going to sleep automatically under High Sierra. Anyone have similar issues or have any suggestions? I have tried resetting power and display settings, unplugging and rebooting etc... nothing.

 

[iScotsman]

Some times sleep takes about 4 or 5 tries with my 2014 mac mini. This started with 10.12 and continues today. With the last update now my mac is freezing and rebooting every couple of days. might as well buy a pc now