Background Information
After you create a new master project, insert one or more projects as subprojects in the master project, and then save the master project, the subprojects no longer appear in the Project Center page in Project Web App (PWA).
Resolution
Navigate to the Project Center page in PWA. In the Show/Hide section of the Project ribbon, select the "Subprojects" checkbox to display all projects that are subprojects of any master project. By default, the "Subprojects" checkbox is NOT selected in Project Server 2010. If you select the "Subprojects" option, however, the system leaves the option selected every time you return to the Project Center page.