For some projects, no trend graphs are shown, even though I have configured Maven to generate the reports (pmd:pmd pmd:cpd org.codehaus.mojo:findbugs-maven-plugin:findbugs checkstyle:checkstyle) and configured the projects to have all these checked:

Publish Checkstyle analysis results
Publish FindBugs analysis results
Publish PMD analysis results
Publish duplicate code analysis results
Scan workspace for open tasks