I’ve posted a few times on this based on my experience with an Edge 605. As far as I can work out the problem is that ‘turn by turn’ routes work off a limited number of points so the Edge guesses which are relevant and throws away the rest (sometimes joining up points which were not even next in sequence).
HOWEVER, when in South Africa last year I was given a 60km tracklog that had been recorded on a Garmin which I was able to navigate perfectly. Can’t replicate it on anything I create though.
General advice seems to be to use Courses but they have their own problems – see my other posts.