Install Nexus Repo 3.18.0, and add in the community R plugin. Create a hosted R repository, and upload a CRAN package to it.
Observe that the PACKAGES.gz file can be downloaded successfully:
Now upgrade to version 3.20.1.
Attempts to download the PACKAGES.gz file fail with a 404 response.
To fix this, it seems to be necessary to upload a new CRAN package to the hosted repository, this triggers a rebuild of the PACKAGES.gz file:
2020-01-10 12:41:26,768-0600 INFO [event-6-thread-13] admin org.sonatype.nexus.repository.r.internal.hosted.RPackagesBuilderFacetImpl - Rebuilding R PACKAGES.gz metadata for repository r-hosted
Expected: The upgrade shouldn't remove the PACKAGES.gz file, or (if that is indeed necessary) it should rebuild it.