Grub hangs if no key is pressed

[Jürgen Bausa]

I have a Xiaomi Air 12 with deiban stretch (amd64) installed. Grub 
(2.02~beta3-5) works in principle but I found out, that it hangs very often, 
if no key is pressed (timeout for selecting the boot option).

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. 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.

I have no idea how to debug this. Is there a debug option for grub that 
enables some output on the screen?

Any other hints?

Regards,

Jürgen