Intermittently (relatively frequent) when the MacBook wakes from sleep and it kicks the external displays on, one or all of them may be fuzzy like this. I have one display in a Thunderbolt port, and the other one is Apple HDMI adapter in the HDMI port.
I've ruled out the adapters being the problem, I've done a PRAM reset. (even after it booted from PRAM reset it did it at boot up on login screen)
To fix it, I have to unplug and plug it back in and cross my fingers that it doesn't happen again.
MacBook Pro (Retina, 15-inch, Late 2013) 2.3 GHz Intel Core i7 8 GB 1600 MHz DDR3 Intel Iris Pro 1536 MB