grub crashes and restarts after an update

[Ishai Asa]

Hi All,

I'm using the Debian testing distribution. Few days ago a new grub version
was pushed and I installed it, all seemed well as per usual updates.
During the update it asked whether to keep overwriting a few grub scripts.
Maybe that has to do with grub customizer gui?

After the restart the grub bootloader menu shows for a fraction of a second
and restarts.
I'm able to boot to windows through the BIOS boot chooser.
I tried using a boot repair disk , but it did not help.

The files on the boot partition (unencrypted) and / (encrypted) seem to be
fine.

How do I find out what's not working with grub? How do I fix this?
Thank you for your help!