Hi Whispered Shadow,
Try recreating the custom themes by deleting the existing themes and check the result.
Step 1: Delete the existing themes and download new themes
a. Right click on the Desktop and click Personalize.
b. Right click on the custom theme and click Delete.
c. Click "Get more themes online" and download the themes.
d. Check if the issue persists.
Step 2: If Step 1 fails, then try to delete the Themes folder in safe mode
a. See Start your computer in safe mode
b. Open C:\Users[Your user name]\AppData\Local\Microsoft\Windows and delete Themes folder.
c. Start the computer in the normal mode and check if the issue persists.
Step 3: Run SFC (System File Checker) scan to find and fix missing system files
a. Visit http://support.microsoft.com/kb/929833
b. Run the scan successfully.
c. Restart the computer for the changes to take effect and check the result.
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