Hey everybody! So my move to Mojave has been quite the experience. Let me explain my use scenario. Before Mojave I had the following setup: GT120 + RX580 This allowed me to access my boot screen on a separate monitor and my RX580 would run my 2K monitors. Everything worked like a dream and I very very often need to boot into different OS's. The Boot Screen selector was a daily use for me. The thread(s) here1 here2 explaining other methods of booting without using an EFI compatible card has not resolved my issues so I decided to upgrade the GT120 to the GT640 which is an EFI + Metal compatible card that would give me the same use scenario back as before. Access to the boot screen on a secondary display. I installed the GT640 got access to my boot screen again (hell yeah) and then fired up macOS. Once I got to the login screen all the monitors connected to my RX580 didn't have a picture. They had (and still have) a backlight just showing a black screen and in the OS are taking up real space. I can send my mouse into the other screens, see them in the System Preferences screens section and I can screen share into my desktop from my laptop and see that all the screens exist. BUT the monitors don't display the screen's image. I have tweaked and played with every option I can think of. When I take the GT640 out and boot again all the monitors connected to my RX580 work no problem (but I lose my boot screen). Pop the GT640 back in with the RX580 and the screens connected to the RX580 play hide and go seek on me again. Even more interesting is this: I booted into Windows (from my newly found boot screen using the GT640!! ) and the two monitors connected to the RX580 were also inactive. So I went and downloaded AMD's drivers and installed them. Boom instantly all 3 screens now came to life. All the screens connected to the GT640 and the RX580 work perfectly in Windows now. Before installing the drivers I cannot remember if the screen space actually existed or not, I don't think it did, but once I installed the drivers everything worked great! Apple makes the drivers for the Mac, there are no downloadable AMD drivers so I am posting this issue here to see if there is some kind of resolution in the works or if anybody running 10.14.1 can try this dual GPU set-up out and let me know if it works in the next update of the OS (which would be amazing.) If anybody else find this odd and want's to reach out to me directly. I've got this posted on the MacProUpgrade FB channel as well. I honestly cannot figure out how to resolve this issue and it's driving me crazy. Any help would be appreciated.