AW: There are several causes that may lead to such behaviour. Please check the place and position of your GPS-receiver which is usually behind the windscreen on the dashboard. The fixation of the GPS-receiver may have suffered due to vibrations and bumpy roads. Another reason can be your park position or parking time (extended period, metal constructions or concrete walls may cause interferences such as reflections and shield your receiver from GPS satellites).
Please note that the device should establish a stable GPS signal before you start to drive around. Otherwise the system could be busy to complete the sat-fix process, which may impact the route guidance accuracy until completed.