In Repository Manager 3 you may see WARN level log messages in your application nexus.log that contain text like this:
CacheInfo missing for ... assuming stale content.
Builds may be receiving 502 HTTP status code responses when accessing a NXRM proxy repository directly.
Builds may be receiving a 404 HTTP status code when accessing a group repository when this happens. The group repository contains a member proxy repository where the content is expected to be found.
One cause of these messages is if the request is trying to resolve the requested content from a Proxy Repository ( either directly or via a group repository) and the settings for that proxy repository have the Blocked checkbox selected, like this:
In that case, determine why the repository was explicitly blocked by an administrator. Unblocking the repository should resolve the issue assuming the remote being proxied can be reached and the missing content can be downloaded from that remote URL.