Answer
Multiple reasons exist for GPS Jamming which are unlikely but could easily cause the issues.
- A GPS jamming device in the vehicle is blocking GPS signals (could be coming from a location around the area you are).
- The vehicle is travelling in an area with dense foliage
- The placement of the GO Device, where the GO device may be physically located in an area where GPS signals are obstructed
- Thick walled materials such as metal (steel) plates
- Near to an electronic device that causes an electromagnetic interference, such as radios or cameras
For the last point, changing the installation location should definitely improve the GPS reception.
Additional Notes
More information can be found in the Geotab blog article: What are GPS jammers and how do you combat them?