The reports are grayed out due to a disconnect between the Project status and the Design Summary viewer. The Design Summary indicates a different Module is set as the Top Module rather that the actual top module of the project.
The detailed reports have been generated and have file names that include the module name (e.g., top.syr, top.bld, top.mrp, top.par). However, in Design Summary, the "Implementation State" indicates "New" meaning the flow has not yet been run with the module it believes to be the top module.
Since the reports with the incorrect top module name do not exist, the report selection appears as disabled and the Detailed Reports table is empty.
NOTE: The the "Errors and Warnings" message files (Synthesis Messages, Translation Messages, etc.) continue to be enabled regardless of the different top module name because these report file names are always static (xst.xmsgs, ngdbuild.xmsgs, map.xmsgs, etc.). So, even with a new top module name, these reports continue to exist with the same names and will be regenerated for the new top module name with the same names.
Changing the top level module to a lower level module and then changing the top level module back to the original top level module has been found to fix this issue.