Comment # 7 on bug 1129027 from Takashi Iwai

(In reply to Stefan Dirsch from comment #6)
> Seems to be the culprit here.
> 
> [    41.914] (EE) modeset(0): failed to set mode: Invalid argument

Yes, looks suspicious.

Could you boot with drm.debug=0x0e boot option on Leap 15.1 kernel with
modesetting driver, and take the kernel messages (the output of dmesg) after X
fails to start?