Difference between elapsed and moving times

I have a new forerunner 245. I've run a couple of 5ks in the last week and, on both occasions, my moving time (& total time) has been circa 8 seconds less than the recorded race time. The race time accords with the elapsed time (not a chipped race). Although I have auto stop "on" I definitely do not stop or come anywhere close to stopping so am unsure why there is a difference? The only explanation I can think of is that the 'moving' time relies on GPS and, given the route is heavily wooded, the GPS signal is lost momentarily during the race. I've run this same park run race before on my old garmin (75?) and it was always accurate so don't think it is connected with the race timing. Any thoughts?