Two issues have been seen that cause this problem.
For Example: The project has a top module name of "top1". However, the Design Summary index has disabled reports, which seem to be referencing a different top module name of "test".
This is evident by selecting any of the disabled reports and choosing "Edit Definition" from the right-click menu.
The resulting dialog shows the name of the file that Design Summary is expecting to find in the current directory. In this case, none of these files exist because they are using an old or previous top module name (test) that is no longer valid.
Xilinx has not been able to determine any specific sequence of events that causes either of the above situations, but, generally, when customers have reported this issue, they have recently changed top modules or added or removed a source from the design (causing a hierarchy re-parse).
To manually correct the issue, select each report in the index (even though it is grayed out, you can still select it) and choose "Edit Definition" from the right-click menu.
You can then change the base name of all of these reports from the incorrect, for example, "test" to the correct, for example, "top1" module to get the correct full filename, for example, "top1_map.xrpt"). If the corresponding file does exist in the directory, the report will be found and will now show up as enabled (rather than grayed out and disabled).