Posted this on another site, but here is the fix:
I have fixed the lock screen loop by the following procedure:
1. Hold <Shift> key and click restart on lock screen.
2. Navigate to Troubleshoot -> Advanced Options -> Startup Settings -> Restart
3. Choose option 5 with the <5> key.
4. Right click the Windows button and choose Powershell (Admin)
5. Run "cmd"
5a. "sfc /scannow"
5b. "dism.exe /online /cleanup-image /scanhealth"
5c. "dism.exe /online /cleanup-image /restorehealth"
Note: If you have not done any theme customization, skip to Step 7.
(This requires you to delete all of your theme settings if you have anything custom)
6. Right click the Windows button and choose Powershell (Admin)
6a. "cd C:\Windows\Resources\Themes\"
6b. "ls" (This shows you what is here)
6c. Find the theme that your computer is using, or look at all files with ".theme"
6d. Move all those files that are not except "aero.theme" as follows:
"mv <name>.theme <name>.bad" (The extenstion doesnt matter, just make them the same, usually folders anyway.)
6e. Replace those names with aero as follows:
"cp aero.theme <name>.theme" (Do this for every other theme you moved, exactly as the names were)
6f. Remove all of the custom themes that might have caused an issue as follows:
"rm .\*.bad" (or whatever suffix you gave them all)
7. Right click the Windows Button and go to -> Shut down or sign out -> Restart
8. When your PC restarts, it should come to the same lock screen that it was stuck on but now logging in works as intended.
9. Be Relieved.
