In analyzing this over in Bug 1731490; grub-install does not check the filesystem of /boot; even if it did, it still needs to do the follwing:
1) copying the proper modules into /boot/efi/EFI/ubuntu/x86_64-efi/<module>
2) updating /boot/efi/EFI/ubuntu/grub.cfg to insmod the required modules for the the search.fs_uuid to locate root/boot
In analyzing this over in Bug 1731490; grub-install does not check the filesystem of /boot; even if it did, it still needs to do the follwing:
1) copying the proper modules into /boot/efi/ EFI/ubuntu/ x86_64- efi/<module> EFI/ubuntu/ grub.cfg to insmod the required modules for the the search.fs_uuid to locate root/boot
2) updating /boot/efi/