The latest release of the free WordPress plugin Redirect URL to Post adds a new parameter: rutdebug. When you apply it, the plugin will show you some information about what is going on when trying to find a matching post.
If you use the value rutdebug=2, you will also see relevant parameters of the database query.
Since this information is accessible from the frontend, we expose no internal or critical data. Everything visible here can be inferred from the URL parameters. The resulting link is exactly what we would normally redirect to.
rutpdebug=1 
rutpdebug=2