I recommend:
- configure geoclue to ignore all sources other than GNSS (GPS) e.g. not WiFi and not cellular - that way you are sure where location information is coming from
- review all existing topics about verifying that your GNSS is initialised properly (downloaded ephemeris) and correctly deriving position information - you may be implying though that this part is working correctly already
Obviously it also depends on the state of your Hardware Kill Switches. For testing purposes you may want WiFi/BT - off; cellular - off; camera/mic - on.