If the GPS trackers are transmitting well but no positions are being sent at the same time, this may be due to several phenomena specific to devices using satellite positioning systems.
The main losses of positions come from the signals dropping out between the GPS tracker and the satellites, thus preventing the triangulation of the position:
– From GPS fix just after departure, cold, where the GPS plotter could not see the constellation of satellites, and therefore needed about 3 minutes before starting to move to find the position and thus start to fix its position correctly.
– The outdoor environment: trees, buildings and even clouds can prevent the proper reception of data from a satellite and may cause triangulation to be prevented or accuracy to be lost.