Once the repair process is completed, restart your computer.
However, if the error persists, then you should resort to the repair method. The fix mentioned above may have solved the Avast error on your system. How To Fix Avast Antivirus UI Failed To Load Error?
Hopefully, you won’t see the Avast Antivirus Failed to load UI error again. After following the fix mentioned above, restart your computer and launch Avast.