I having a problem waking my external Dell P2715Q monitor which is plugged via display port into my MacBook Pro in clamshell mode (while the lid is down). After waking the rMBP by clicking the mouse the external monitor indicates a wake-up state, the monitor power light stays lit for a few seconds with a blank screen - indicating that it's received some sort of signal from the rMBP - but then after a few seconds the monitor often returns back to a sleep state. However, when I open the lid on the rMBP it often wakes up both the rMBP and external monitor and everything is fine.
My question is - why do I need to take the rMBP out of clamshell mode to do this? This never used to be the case. I used to be able to just click the mouse and both the rMBP (in clamshell mode) and external monitor would wake up.
I'm not sure if it's the monitor or MacBook Pro's signal feed to each other, or if it's a macOS thing, which is the culprit!?!
My question is - why do I need to take the rMBP out of clamshell mode to do this? This never used to be the case. I used to be able to just click the mouse and both the rMBP (in clamshell mode) and external monitor would wake up.
I'm not sure if it's the monitor or MacBook Pro's signal feed to each other, or if it's a macOS thing, which is the culprit!?!