There are a few reasons as to why you may notice that you're receiving Unknown Location data for the opens you get after you've sent your tracked email. The publicly available IP location information is necessary to address the opens and provide you with the location data on said opens.
For Mobile devices, this data will come from the nearest Cell Tower. Generally, you won't see any issues with the IP location for mobile opens.
For Desktop devices, the IP address shown/geolocated would be based on your local network. In the case of an unknown location this data is likely coming from your Mail Server with an obscured IP address.
This is an internal function within your company, you can discuss possibilities in accommodation with your Mail Admin Team.