Ever since we've upgraded to Sonatype Nexus 3.x we are missing our custom archetypes in the repository.
When browsing to http://repo/repository/maven-releases/archetype-catalog.xml I am being shown an empty archetype XML:

I have tried rebuilding the index of the repository and also tried deploying a new archetype version, but nothing seems to populate the archetype-catalog.xml. The catalog was working with version 2 of Nexus.