Grub2 updates for Red Hat systems are making some unbootable

Now that this has been fixed (https://access.redhat.com/errata/RHBA-2020:3265 and https://access.redhat.com/errata/RHBA-2020:3262), does anyone know what was the bug? I haven't seen any official announcement or blog post explaining what went wrong.

The only thing I have found so far is https://git.centos.org/rpms/shim-unsigned-x64/c/834e5a0c4... ("[PATCH] hexdump.h: fix arithmetic error") which mentions fixing rhbz#1861977 (https://bugzilla.redhat.com/show_bug.cgi?id=1861977).