Grub crashes with dual monitor connected to intel uhd 630 internal gpu

[Klaus Rudolph]

I run a "Intel(R) Core(TM) i5-8400 CPU @ 2.80GHz" with internal UHD 630
GPU. If I connect 2 monitors to the system, grub seems to be crash
before it displays the boot options. Booting with a single monitor,
independent if I use HDMI or DP interface, everything works fine. Both
monitors have resolution 1920x1080.

If I connect the second monitor after linux kernel takes control,
everything works fine.

I can't tell if I only "can't see" the boot menu because graphic device
simply did not display it or if grub crashes already before.

After a few seconds system goes to warm-boot and comes back after some
loops with bios setup. Seems to be that bios recognize that booting will
not work which is the good thing.

As I can not see anything during start up of grub, I need some advice
how to get some debug information which enables you to find the
underlying problem. I know that "did not work" will not help anyone here.

So it would be nice to get some advice for getting debug output, maybe
via serial connection or other method. If needed, I can setup a separate
harddisk to play around also with patched code if that helps.

As I can not interact with the grub cli, I have no chance to add some
parameters for booting, but as said, it seems to be crash is before
coming up for first grub menu output.

From "bootinfo" script I got:
 Grub2 (v1.99) is installed in the MBR of /dev/sdc

I also tried newest fedora live image ( Fedora 30 ) and the behavior is
the same. I did not know which grub is in use there.

My current system is Fedora 29 updated more or less daily.

Sorry for only minimal information here.

Regards
 Klaus