This is due to errors in positioning, let us say that when stationary you 64 marks a position, then a few seconds later it incorrectly plots a new location a few metres to the North, followed by another incorrect plot that is a few metres West of that second location and finally a third location that is the same as position 1, the GPS thinks you have walked in a triangle with sides of a few metres + a few metres + a few metres, this random plotting of errors happens on all GPSs, with the errors getting bigger when the satellite signals are poor
You can stop this happening by only allowing the GPS to plot a new position if it think you have moved by a certain distance, say 30 metres, then all small movements will be ignored
Menu >> Menu >> Setup >> Tracks >> Record Method >> Distance >> Recording Interval >> 0.03km