The most common reason is that the daily lookup limit has been reached. Free users can perform up to 500 IP lookups per domain per day. Once that limit is reached, Geo Controller stops returning geolocation data for that domain until the quota resets the following day.
Empty geolocation fields can also be caused by visitor IP detection issues, proxy or CDN configuration, temporary API availability problems, or another configuration issue.
Check the Geo Controller sidebar inside the plugin settings and the Debug page first. These areas provide status information that can help identify why geolocation data is unavailable.
For details about how lookups are counted, caching, daily limits and unlimited licenses, see the How does lookup work? documentation.