Community Edition with VSTS: To use the property "sonar.branch.name", the branch plugin is required but not installed

Thanks. The first thing I recommend checking then is that the SonarQube task (and the build definition that contains it) is only triggered on master branch. Community Edition does not support analysis of branches, so you need to make sure that SonarQube analysis only is performed on master (we’ve took a note here to make the documentation a little bit clearer in that aspect).