Are you sure that, the log that you are expecting are not just... from Microsoft nameSpace ?

You put :

 lc.MinimumLevel.Override("Microsoft", Serilog.Events.LogEventLevel.Warning);
 lc.MinimumLevel.Override("System", Serilog.Events.LogEventLevel.Warning);

If you were excepting a log saying now listenning to some port or something, these are Information level from Microsoft.* namespace