I've got an old Magellan hiking GPS unit. One of the hikes I did last year showed a distance of many thousands of miles; what happened was exactly what you're talking about. Zooming in to look at the map, it shows me walking the trail, then for a moment I'm 50 miles away on a different trail, then I'm back on the one I was actually hiking. Same type of error many times, and the end result was nonsense.

I've been using the new Fenix 3 watch, and it has an entirely different GPS issue. It's never put my in the wrong county, but, instead, it cuts corners. It's like the thing can't accept or believe that I did a 90 degree turn, so it rounds it out some. It's still wrong, but it's an entirely different kind of wrong. Not that the system just had a glitch and I teleported to China for a split second, more like the software that asks "does this point make sense?" got it wrong. Here's what I'm talking about, I recorded these two GPS tracks together at the same time:





It's ironic and slightly disappointing that the brand new Fenix 3 isn't as good as the 5-year-old Edge 800. How does your Ambit 2 track?