No image after sleep/hibernate and can't turn off monitor (dual u2723QE MST setup)

When my machine wakes up from sleep/hibernate mode than both monitors don't provide an image (no signal DP). Also I can no longer power down the main monitor, I can power down the 2nd monitor (both u2723qe in MST setup via DP).

I can resolve this issue by removing and reconnecting the power cable from the main monitor. However, this is far from the intended methodology! 

Does anybody have any ideas how to resolve this issue.