GameCenter achievements not always reporting

To start, sandbox gamecenter is configured correctly. Leaderboard posting and achievements that report 100% progress as a full unlock work.

I just now am seeing failures on the fractional reports for incremental achievements.

Anyone have tips on how to get some deeper info through xcode's debugger to potentially see whats failing inside GameKit.framework? Or any other paths to take?

 

So resuming troubleshooting this morning, I found the following:

1] I added in a call to GameCenterPlatform's ResetAchievements upon app start for testing
2] The FIRST time any achievement where ReportProgress is called (whether its 100 or 0.2 progress) it works
3] Any subsequent calls for the same achievement id's fail (reporting another 0.2 to increment overall progress to 0.4 fails or even reporting another 100 progress fails)

It almost seems like GameCenter won't perform the progress summation serverside. Is that the case? Do we need to retrieve the current achievement progress on sign in and maintain that during gameplay (and in success callbacks increase the progress as well)?