Win10 "spotlight" lock screen was stuck on single image, now blank and no image ever gets displayed

To first check for Windows corruption, do the following:

• In Settings > Privacy > Background apps, Microsoft Edge should be turned On
• Run sfc /scannow
• Create a new user account and check if the problem exists in it. If not, there is a profile corruption. You will need to transfer all your personal stuff to the new account and work with it, as finding the cause of such corruption is extremely hard.

If no corruption was found, the list below contains the known fixes to Spotlight. If none of them works for you, then Windows is corrupted and will require Repair Install with an In-place Upgrade.

Method 1

1. In Start > Personalization >Lock Screen, change Background to Picture, but do not exit Settings
2. Delete everything inside the folder %LocalAppData%\Packages\Microsoft.Windows.ContentDeliveryManager_cw5n1h2txyewy\LocalState\Assets (but not the folder itself)
3. Open in Explorer the folder %LocalAppData%\Packages\Microsoft.Windows.ContentDeliveryManager_cw5n1h2txyewy\Settings
4. Inside the folder, rename the files settings.dat and roaming.lock to settings.dat.bak and roaming.lock.bak
5. Reboot
6. In Start > Personalization >Lock Screen, change Background back to Windows Spotlight

Method 2

This is a stronger version of the first method.

1. In Start > Personalization >Lock Screen, change Background to Picture, but do not exit Settings
2. Delete everything from inside the folder %LocalAppData%\Packages\Microsoft.Windows.ContentDeliveryManager_cw5n1h2txyewy (take backup)
3. In Lock Screen settings, change Background back to Windows Spotlight
4. Reboot

Method 3 : Using PowerShell

1. In Start > Personalization >Lock Screen, change Background to Picture

2. Run PowerShell as administrator

3. Type the following command :

   Get-AppxPackage -allusers *ContentDeliveryManager* | foreach {Add-AppxPackage "$($_.InstallLocation)\appxmanifest.xml" -DisableDevelopmentMode -register }
   

4. Reboot

5. In Start > Personalization >Lock Screen, change Background back to Windows Spotlight

I have found the issue! Permissions on this folder were broken/incorrect (this was my fault because this is where I deleted the stuck image from): C:\ProgramData\Microsoft\Windows\SystemData

Manually deleting all the corrupted sub-folders under the SystemData folder, then re-adding SYSTEM with full-permissions on the SystemData folder. This allowed the lock screen images (single image, slideshow, or Spotlight) to again function normally. If you have this issue you may need to also perform the steps @HarryMC listed above.