LED Monitor not waking from sleep

Maybe someone has a seen same or a similar issue...
Mac Mini 2014 running 10.10.5.
All of the computers were migrated using Carbon Copy Cloner to new hardware. I booted from the CCC backup image to each new 2014 Mini without issue. I reinstalled/repaired 10.10.5 on all machines having the issue to hopefully get all hardware specific settings in place.
The issue is that with 2 external monitors and the 2014 Minis go to sleep. When the user comes back to the computer one of the monitors doesnt wake/stays amber. I believe its always the monitor attached to the Apple branded HDMI-DVI connector that came with the 2012 Minis that the 2014 Minis replaced.
When I turn off all sleep settings, there doesnt seem to be an issue.
How best to troubleshoot and fix?
Any help is greatly appreciated.