This is usually because the device is not properly connected to the GPS satellites and therefore shows the last recorded position. The lack of connection can be caused by the tracker being indoors, placed under very thick material, such as thick metal, that prevents the signals from reaching it.
To fix the problem, ensure that the tracker has access to power and then shake the device outdoors to help it connect more easily to the GPS satellites. Also, double-check that you have an active data plan for the tracker.