This counts join and leave messages the device discarded because they arrived on a host-facing interface while no multicast router interface had yet been established for that service, meaning the device has nowhere valid to forward that membership information. An admin seeing this counter climb on a newly configured service would check whether the router-facing interface configuration, or dynamic router discovery, is actually working, since receivers can be actively trying to join while the device has no functioning upstream path to satisfy them. A steadily growing count here on an otherwise-new service would point directly at a missing or failed router-interface setup as the root blocker.