It is likely this bug is the same as the one reported upstream at
https://savannah.gnu.org/bugs/index.php?65503
I'm citing below the workaround that is mentioned there
https://savannah.gnu.org/bugs/index.php?65503#comment2
> As a follow-up to my previous comment (in case anybody is listening),
> I found out that I could also work around the issue by printing
> anything on the console, before switching to gfxterm (so, without any
> delay). E.g. with the following:
>
> echo "Loading bootloader..."
> terminal_output gfxterm
Adding only the 'echo "Loading bootloader..."' line at the beginning of
/boot/grub/grub.cfg works too.
