Problems with DELL P2415Q monitor not waking from sleep.

I have two Dell P2415Q monitors hooked up to a MacPro (2013). I've followed the proper procedure to connecting them to the display port buses, etc.

The monitors work fine while they are on. Though I've noticed since upgrading to Yosemite that they do not properly awake after going into energy saver mode. My machine is setup to not go into sleep. Just put the displays to sleep after 10 mins.

At completely random times when I go to wake up the displays (hitting a keyboard key), one or both do not wake up. The Lights in the corner remain white and nothing appears. Even a restart doesn't seem to help, it's as if they are locked in a "deep sleep".

The only way to remedy the situation is to unplug the monitor power, and plug back in. Last night both got stuck, and I had to perform this fix on both individual – in other wards, neither reacted to the fact the other was "awakened".

I looked through the Dell settings and the energy saver settings are sparse at best.

Does anyone have any similar experiences with this or other displays recently?

Thanks!

Steve