grub hangs on timeout

[Jürgen Bausa]

I have a Xiaomi Air 12 with debian stretch (amd64) installed. Grub 
(2.02~beta3-5, legacy mode, disk is gpt with ext4) works in principle but I 
found out, that it hangs, if no key is pressed (timeout set to 2 s for 
selecting the boot option) and the default graphics resolution (1920x1080, 
which is listed by vbeinfo as a possible resolution) is used.

In this case the default option is correctly selected. Then, the screen is 
cleared, the name of the selected kernel is displayed and the message "loading 
initial ram disk". Then the screen gets black and nothing happens anymore (I 
waited for half an hour). It seems that the system is never started (nothing 
is written to the logs).

If I select the default boot option by pressing <Enter> on the first grub 
screen, everything works fine and the system boots up normally. However, I 
noticed that grub is very slow if I press an arrow key. It takes about 1-2 s 
between pressing the "down" key and the reaction on the screen.

If I set a smaller screen resolution (e.g. 800x600), a text console or if I 
set a higher timout (e.g. 5 s) everything works fine (race condition?). Using 
this workaround I can run my system but I think this is a bug in grub which 
needs to be fixed.

Regards,

Jürgen