Tracing turned on and pointing to a non-existent folder or a folder to which the user account does not have full permissions without UAC prompting.
We have seen cases whereby an alternate path for diagnostics logging in the Windows Login Provider system was specified but did not actually exist. This caused the Windows Login Screen to either present a black screen with no login options or no ability to see the login screen after dismissing a pre-login notice.
To prove the issue, the customer had specified a subfolder under the default path of c:\windows\temp and then later deleted that folder. Because tracing was enabled and the subfolder was the target path for logging, the provider was unable to write the logging into the path and this caused a fault, crashing the provider by way of the DEP system that is on by default in Windows 10.
Avoid changing the diagnostics path without verifying the new path exists and is writable. Also, avoid enabling diagnostics logging unless needed for troubleshooting. We also suggest maintaining remote access to the registry and/or file system when testing and using diags to be sure you have the ability to recover should this situation arise.