Comment 7 for bug 1635906

I was able to permanently (I hope) fix the problem.
After reading around, examining system files, logs and a lot of guesswork, I noticed that /usr/share/X11/xorg.conf.d had amdgpu configuration along a bunch of others but no intel. So I tried to find a sample file on the web and created (as root) 20-intel.conf containing:

Section "Device"
   Identifier "Intel Graphics"
   Driver "intel"
EndSection

rebooted, and a miracle happened! It loaded with both external monitors working again! Lost the configuration though, but after redoing monitor arrangement etc and rebooting again it was all good. I hope this helps someone.

Regards,
isotope.