Why do the compliance graphics on the Overview page of my report show less than 100% compliance, even though when I go to the Modules page, I don't see any violations?

The compliance graphics on the Overview page reflect the compliance of your overall organization, not of an individual report. Therefore, you might have a project that is fully compliant, but if there are other projects in AMP that are not fully compliant, the compliance graphics in the Overview will not show 100% compliance.