Previously I have used the Skymap IIIC which was generally reliable but did on one occasion near Reims indicate that I was flying to the left of an Autoroute when I was in fact on the right.
You will find this with any solution that uses vector-generated maps, including SkyDemon. There is simply no room on your device to store the exact lay of every major and minor road, to the nearest cm. If you're lucky they'll store major roads, and build it up based on position fixes every km or so. Inbetween these position fixes the map will be off, and that may well mean that the device indicates you're flying on the left, while you are really flying on the right of the road.