GRUB not finding Windows 10 bootloader

[BenJuan26]

I recently migrated my Windows installation from a SATA SSD to a larger M.2 SSD using system image recovery. The migration went well as far as I can tell, and when I boot straight into Windows, it works fine.

 

I also migrated my Arch Linux installation from an HDD to the SATA SSD that used to hold the Windows installation. I used rsync to replicate all the files, and then did arch-chroot and got the bootloader installed.

 

For a few boot cycles, everything actually worked. Grub found the Windows installation on the new drive and pointed to it, and I could pick either Windows or Arch in the Grub menu, and they would boot just fine. At some point, though, Grub stopped finding the Windows installation. It finds it during os-prober, but not during boot. This is the error I get at boot time:

error: no such device: 322CF7B72CF77467.
Setting partition type to 0x83
error: invalid signature.

I eliminated a few possibilities. Both OSes are using MBR and BIOS. According to both blkid and /dev/disk/by-uuid, that's the correct UUID for the Windows partition. I've used both Grub Customizer and straight-up os-prober and they both see the Windows installation and point to that same UUID, but still no dice at boot time. And again, if I hit F8 to get to my BIOS boot menu, and boot from the M.2 directly, Windows boots up fine. So nothing is broken badly, and I can still get in to both OSes, but why would Grub have trouble finding Windows at boot time? Again, this was working for a while and then stopped.

 

I've attached my grub.cfg below, but here's the relevant stuff for Windows:

	insmod part_msdos
	insmod ntfs
	if [ x$feature_platform_search_hint = xy ]; then
	  search --no-floppy --fs-uuid --set=root  322CF7B72CF77467
	else
	  search --no-floppy --fs-uuid --set=root 322CF7B72CF77467
	fi
	parttool ${root} hidden-
	drivemap -s (hd0) ${root}
	chainloader +1

I briefly tried commenting out the search and doing set root='(hd0,msdos1)' directly, but that came back with a different error, and I don't know whether that's even the right track or not, so I stopped there and put the search back in.

grub.cfg