That would go to the regular log file. For UWP without a cook server this is %localappdata%\Packages{Package_Family_Name}\LocalState{Project_Name}\Saved\Logs{Project_Name}.log. You should also see it in the Project Launcher output window if running using the Project Launcher, or in the debugger output window if running under the debugger.
Sounds, though, as if an error is not the problem. I suspect the stat is not actually getting the ‘Feature on players’ profile’ flag, and it sounds as though there may be no way to apply that in the current UI for Creators Program titles. Have you had a chance to try retrieving the stat in your own code yet, (e.g. via StatisticManager::GetLeaderboard)?