External Monitor Won't Wake from Sleep

Main Mac = iMac Pro

External Monitor = iMac mid 2011 (27inch)

Connection via Thunderbolt 2 cable with Thunderbolt 2 to 3 adaptor on iMac Pro end.

All cable and adaptor from Apple

iMac mid 2011 won't wake from sleep

Work around = press CMD F2 again (only works on original apple keyboard)

It will wake the external monitor and exit the external monitor mode,

Just press CMD F2 again to get iMac mid 2011 back to external monitor mode

Don't need to unplug cables

Don't need to reboot

Tried to press power button on iMac mid 2011 before, but didn't work

hope this helps.