Windows 10 Cumulative Updates Failing (On Computer with SSD System Drive + HDD)

I have been having issues with Windows 10's cumulative updates failing for a couple of weeks now. I've tried running SFC /scannow, I've tried running using DISM to replace corrupted system files, I've tried downloading the update and running it manually, I've tried running an in-place upgrade (Windows 10 Pro x64 to Windows 10 x64 upgrade, so wouldn't lose programs or settings) (which failed, by the way), and I don't even remember what all else I've tried, all to no avail. There doesn't appear to be an answer to my specific problem anywhere on the internet.

My computer is running Windows 10 Pro 64-bit.

I am also running a solid-state drive (system drive) and a hard drive. I've got the folders inside C:\Users linked to a location on the HDD with directory junctions to save space on the SSD.

Answer

The reason for this is that for some reason the update has to copy files to one of those folders that is symlinked, and is unable to do so. It is looked at %systemdrive%\Users[whateverfolderhere] and is for some reason unable to move the file to where the Directory Junction is pointing.

In order to fix this problem, following these steps:

1. Open regedit (press Windows Key + R, and type "regedit)".


2. Browse to HKLM\Software\Microsoft\WindowsNT\CurrentVersion\ProfileList.


3. On the right, there are keys with "Data" values pointing to where different Profile folders are located. It should look something like this:
   


4. Change "%SystemDrive%" under "Default," "ProfilesDirectory," and "Public" to the correct drive letter (the drive letter for the HDD). In my case, this is drive D:
   


5. Restart your computer and try installing the updates again.

Just remember to change this if you ever change drive letters!