I noticed that the CCCC trend chart was missing on a few projects that I have configured to use it. It looks like the matter boils down to the project's CCCC report not being parsed on failed builds ("Parsing cccc results" only shows in the console for non failed builds). That appears to cause no results to be stored for the project.
The trend chart was missing on the projects, because that only appears on the project's page when there's more than one unstable or successful builds. This makes sense for the first builds that use cccc, but not when there's 40 or so configured builds. For ex. say builds A through Z are configured with cccc, and build Y failed, the trend chart only shows results for Y and Z. The chart went missing for projects whose previous build had failed.
Since the project's source files to count are still there even for a failed build and I can still generate a report, it would be good if the plugin would fire off even during a failed build and persist results. Hopefully that will also help resolve the secondary issue with the chart only showing results for the unbroken series of unstable or successful builds.