Very inaccurate KM count

Hello. There is a route that I do very often. It always starts outside my home, and ends at the same point. No deviations.
I can understand that there are differences when it comes to registering the total number of km traveled, but only in the order of tens of meters, not more than 1 km!
Which may be due?
I still think that the speed sensor works very badly, and it always affects the count. But for the last 4 records, I left it on auto for wheel size. Because it never counted me correctly, compared to a forrunner 245.
Thank you