Edit: I just read your latest post. It sounds like your config is freezing on wake, so my suggestion probably won't work.
@pk3 : I'm not sure if this will work, but I was having a similar problem with using the iGPU and the motherboard HDMI out on my motherboard, the related Z390 Gaming X. After waking from sleep, the video signal didn't work. It would only come back after unplugging and plugging the cable.
To fix it, I used the Whatevergreen boot argument
igfxonln=1
. I am not sure if this argument is only for the iGPU. The description is "force online status on all displays" but I don't know if that means all displays connected to the mobo video ports, or all displays.
It's worth a shot!