${project.basedir} points to the submodule directory and unable to collect the coverage of sub-modules correctly.
use ${maven.multiModuleProjectDirectory} instead
${maven.multiModuleProjectDirectory} always points to the maven root directory
correct setting:
<properties>
<sonar.coverage.jacoco.xmlReportPaths>
${maven.multiModuleProjectDirectory}/report-aggregate/target/site/
jacoco-aggregate/jacoco.xml
</sonar.coverage.jacoco.xmlReportPaths>
</properties>