Any errors in the gatherdb logs? Also, from the root server, try browsing to the gather URL in a browser and see whether the page can be loaded, and check the site version from the page if it loads.
I’vevseen several recent postings on gather fails. Often it seems a proxy is either blocking the gather, or returning an older copy from the proxy cache, or modifying the content so the signature no longer validates.
The easiest fix looks like configuring the root server to gather via HTTPS rather than HTTP, which is generally better for everyone anyway.