I have the same problem. Uninstaling the drivers in secure mode with DDU and reinstalling again seems to fix it temporaly, but the problem start again after a few days. I only have 1 display active at a time. The problem seems to occur only in the DVI monitor, the HDTV works fine.
The erros I get:
Stellaris: Failed to create a graphics device. Exiting.
Rocket League: Your video card does not support alpha blending with floating point render targets ...
Don't Starve: Error during initialization.
Rainbow Six Siege: Opens in windowed mode. Cannot change to fullscreen nor change resolution.
Dir Rally: Opens in windowed mode. Cannot change to fullscreen nor change resolution.
Company of Heroes 2: Cannot find supported hardware rendering device. Ensure that you meet the minimum system requirements... verify that DirectX is installed and drivers are up to date
I just find this fix (Enabling GPU Scaling in the Radeon drivers for the DVI monitor [Games not working in DX9/DX11/OpenGL since 17.4.4 on RX 460 in a DVI Monitor. ]) and seems to work, but I don't know for how long.
AMD Graphics Card
AMD RX 480 Nitro+
Desktop or Laptop System
Windows 10 Pro (64-bit)
Driver Version Installed
Radeon Software Crimson Edition 17.4.4 (tried with several)
Dell Ultrasharp U2412M (DVI)
HDTV Panasonic Viera 40'' (HDMI)
Processor and RAM
i5 2500k at stock speed
EVGA 750W G2