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Fixed? Nope. Although I don't know if we've encountered this situation again since I posted here 4 months ago. 

We switched to the basic display driver by accessing the computer another way. I don't recall if we used LabVNC (through CW Automate), or RDP, but somehow we got into the system and changed the display driver to the Microsoft Basic Display Driver using the Device Manager.

Oh, and I forgot to mention we're on Control 19.2.24707.7131 (2019.2). Not the latest version, which is 
19.3.25270.7185 (2019.3), but just one release back. 

We experienced this issue today on 2 identical machines. 

Lenovo ThinkCentre M715q

AMD Ryzen 5 Pro 2400GE

AMD Radeon Vega 11 Graphics (driver version 26.20.11022.3)

Windows 10 Pro 1809 (10.0.17763)

We switched the display driver to the Microsoft Basic Display Driver and Control immediately started showing an image and worked normally. Did the same, with the same result, on both machines.

Any update on this, or a permanent fix?