I had recently followed a guide a guide I found on TenForums that showed how to entirely relocate C:\Users to another volume, by making use of Audit Mode, Sysprep, and an XML script. This is officially supported by Microsoft, topic can be found at:
My setup consisted of a VHD, with 2 volumes within, one for C drive, and the other for Users. Everything was successful, 10 running fine, no issues at all. But then, even though nothing was wrong, I decided to create a new, bigger VHD, same setup as before, but with each volume being bigger. So I used Drive Snapshot to backup my C and Z drives, then proceeded to restore my backups into the newly created partitions. I then created boot files with bcdboot. Both volumes are within an MBR VHD, but 10 boots in UEFI mode, because the boot partition is located on a large GPT drive.
After booting into the OS, everything seems fine, until I enter my password and immediately get the message "The user profile service could not be loaded".
I'm not sure what happened, but either my drive letters somehow got screwed up, or the new VHD's disk signature is different, causing Windows to not assign the correct drive letters. I found an article mentioning that the Registry can be edited offline, and something to do with changing/deleting MountedDevices keys.
I'm not about to reinstall a perfectly good OS that was never corrupt to begin with, help is appreciated.