JBL Navigation system gets confused

The icon on the map that represents where I am has recently become inaccurate. I have re-calibrated the system several times to correct my location on the map. It will stay accurate for a while but at some point it gets confused and starts wandering in another direction. For example, the other day I was driving North, but the navigation system thought I was driving South. My direction of travel was North and the compass showed North, but the navigation system was confused and thought we were going the other way. I have searched around the internet and haven't found anyone reporting this type of behavior. Anybody have a clue?