Monitor with MacBook Pro 2016 not waking up
I had a similar issue.  I have two UltraFine 4K monitors connected to a 2016 MacBook Pro. When the Mac went to sleep both displays went to sleep, but only one would wake.

This has been resolved by the latest firmware.  


Install LG Screen Manager. The LG site is still showing the old version.
It will push the most recent version, v2.06.
Upgrade your monitor to the latest firmware. (3.11, 3.4, 5226, 3.04, 0.2f)




For some unknown reason, LG appears to have removed the LG screen manager tool from their site. If you are looking for the latest firmware, it can be found via homebrew.

brew cask search lg
brew cask install homebrew/cask-drivers/lg-screen-manager