With a multi modules build you can not use: mvn site-deploy. You must stage your site first.
Cli to use: mvn clean site site:stage-deploy scm-publish:publish-scm
<properties>
<!-- override the property in your settings -->
<site.mainDirectory>${user.home}</site.mainDirectory>
<siteContent.path>\${site.mainDirectory}</siteContent.path>
// it's a default location for performance reason (not checkout the content all the time)
// you can override this value in your settings.
<scmCheckout.path>\${site.mainDirectory}</scmCheckout.path>
<siteDeploy.url>file://${siteContent.path}</siteDeploy.url>
</properties>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-scm-publish-plugin</artifactId>
<version>1.0-beta-2</version>
<configuration>
<checkoutDirectory>${scmCheckout.path}</checkoutDirectory>
<content>${siteContent.path}</content>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-site-plugin</artifactId>
<version>3.1</version>
<configuration>
<stagingSiteURL>${siteDeploy.url}</stagingSiteURL>
</configuration>
</plugin>