Comment # 28 on bug 955493 from boo35 boo35

The fact remains ...

Start with a working v13.2 server as described.

Run the 13.2 -> Leap upgrade.

execute grub2-mkconfig to generated a new config

reboot the machine.

you will still drop to an EFI shell, and go no further -- as reported.

That's WONTFIX at best.