While I do normal runs, as well asl programmed workouts, it happens that my pace is completely odd. While I am running 5:30 min/km it will show something like 7:00 min/km and then randomly switch to 4:00 min/km. When wrapping-up the run, it will show the actual pace, but while running it keeps changing, making it impossible to keep a steady pace.
I keep my watch updated and always run with GPS turned on, so why is it, and how can I fix this?