I have noticed in our logs that repman queries a lot of /p2/foo/bar.json files on the main packagist.org domain. Due to some optimization on our end we will need to stop serving those files at some point on the main domain.
The correct domain to use for metadata as per the docs is repo.packagist.org. Please update your default configs so that it fetches from the correct domain as it will eventually stop working otherwise.