Hi devs,
To reduce the pressure on the main http://nexus.xwiki.org and have better response time for the CI, we decided to move Maven SNAPSHOT artifacts to their own Nexus instance on https://nexus-snapshots.xwiki.org. It's also the occasion for us to get more familiar with Nexus 3 before migrating nexus.xwiki.org.
The main impact for you in practice is that you should change the snapshot repository you have in your Maven /.m2/settings.xml so that Maven download SNAPSHOT artifacts from the right server. You can take a look at the now updated documentation on Building.