My two cents. I think it was a combination of issues. Poor satellite could have started the problem. Solar interference could have entered in. I have witnessed my location moving around the map when there has been heavy solar activity.
If a GPS does not have an electronic compass built in you can easily have the always moving in the wrong direction scenario. This type GPS only knows orientation after it has moved enough distance in one direction long enough to calculate the direction of travel. If you are walking east towards your destination and stop and turn and walk west the GPS will allow you to watch the screen and appear to still be on course for a distance. Very confusing I know but something you need to be aware of. I used to watch my compass carefully as I bushwhacked through un tracked terrain. Always being careful to keep the GPS pointed to my goal.
Some of the newer gps's with electronic compass allowed you to set the parameters of when the internal compass would take over from the GPS heading calculation. More hairs lost on that issue. More battery used if the electronic compass is on all the time.