One possibility is that it has a degenerate UEFI implementation that will only recognize the efi “payload” if it’s in the fallback location—I had this problem with an older HP laptop. You can force grub-install to place the needed file in this location by passing the --removable switch (you may also need to pass --efi-directory=[dir]), or you can manually copy the file to EFI/BOOT/BOOTX64.efi on your EFI partition if it was already installed elsewhere.