Comment 5 for bug 1720572

strace shows:

[pid 30986] execve("/bin/efibootmgr", ["efibootmgr", "-q", "-c", "-d"], [/* 35 vars */]) = 0

this points to a problem in grub-core/osdep/unix/platform.c:grub_install_register_efi(), where efidir_disk is being set to NULL.

This suggests that grub is unable to resolve your /dev/md1 to a physical disk.