The accuracy related problems can vary and the main cause is a poor
gps signal. This depend on many factors (your device gps sensor
quality, your position, what is around you - eg. you are on a narrow
street with tall buildings around you).
More exactly, the gps sensor send to receivers (in this case AndiCar)
not only the geographic location (longitude, latitude, altitude), but
also the estimated accuracy of these values.
You get this warning if the accuracy value exceed the maximum allowed
limit for a number of 10 consequent trackpoints. You can adjust the
allowed accuracy limit from AndiCar -> Preferences -> GPS Track ->
Accuracy