GPS inaccurate

Hi folks,

I own a FR970 since mid of August and was quite pleased with the features and the build quality. But recently I discovered that the watch measures distance not correctly while running workout. My usual daily running track is ~5,67 km, but the watch measures between 6 and 6,5km. Rebooting helps for a couple of sessions (~5) and then it starts again measureing the wrong distance. Firmware is 12.72. GPS is on every second (not intelligent) and satellite mode is set to "all + multiband".

I wear the watch everyday and sync automatically.

Any ideas?