You can perform a on-demand location update on the map page if your target device is Android or iOS and is running a paid app. This will send a silent notification to the target device to force a location update. This notification will not cause a popup or alert in the target device.
If this problem does not resolve, you can perform a quick troubleshooting on the map page
in the complete web site (not available in mobile site). Select the device with trouble, and click the link "Don't see your location" under the map. You can also view the tracker errors on the same map page.
If the above quick guide does not help, you can use trouble shooting for the GPS tracking app
Why the app cannot login to the server?