The Sonarqube scanner is ignoring the Server URL parameter in the Jenkins config when querying Sonar for the quality gate status. It is using Sonar's own address instead.
I have an IP address set in Jenkins (as the intranet DNS will not resolve there), whereas for users I have a friendly hostname set in Sonar. Jenkins tries to resolve the friendly hostname instead of the Server URL I specify, which fails, and breaks the build.
I've reverted back to 2.6.x for now.