[Milhouse]

I'm just wondering if the AMDGPU DC flag discussed here: (at Phoronix.com) has anything to do with my problem. Does AMDGPU have anything to do with what is being done with LibreELEC? Was it ever part of any previous Test builds?

There is no AMDGPU DC in 4.14.y, this was only added in 4.15.y. You can try a 4.15.0 LibreELEC build and see if that makes any difference. If you need a more recent mainline kernel to fix this issue then you'll need to look elsewhere as LibreELEC only ships LTS kernels now, which means 4.14.y for the next 12 months or so.