So, my love / hate relationship with Garmin products continues. I do have Glonass enabled and have recording intervals set to 1sec, which is the most you can do. All of my routes look like this since buying this device, none of them actually match up with a map of the area, sometimes not even close. What gives? This is terrible.
This is a road bike ride, we obviously didn't leave the road.
I think part of your problem is the map you compare your route with. I took your second image, near the intersection of Ellijay Rd and Circle D Farm Rd - looks like this place. The road map from Google Maps differs significantly from your Mapbox output, and your GPS track actually matches the Google map version, with the tight switchback on the left. The Google Maps sat view matches with the map track as well. The Mapbox map looks very "creative" in that section. So first part of the problem is solved.
Second, from the sat view one can see this is a relatively tight forest - one can barely see the road on the sat image. These conditions are always difficult for GPS signals, so you get less precision than on an open road; this probably explains the first image, where one of the tracks has a sharp point in the switchback and then cuts the longer turn. This will happen to various degrees with any GPS receiver in that kind of conditions. Using a speed/cadence ANT+ pickup will minimize the impact of these GPS fallouts on your indicated speed and distance, but will obviously not help with the GPS track recording.
So your love/hate relationship with Garmin should bleed into a love/hate relationship with various map sources, and another one with GPS receivers in general...
Perhaps it is somewhat a mapping issue. But, you can change to a satellite view and the tracks don't even come close to following the road in a lot of places that isn't tightly wooded forest area on some of my rides.
On the road bike, I am using an ANT+ speed + cadence sensor actually, and have my watch linked to it. My watch is also mounted on my bars, with as clear of a view of the sky as possible. Oh well, is what it is I guess.
