That shouldn't be happening - could you share the route where you're seeing this issue with us? You can also send us a support ticket to keep the discussion private.
This should reproduce the problem.
Create a new route in the web app, search for a (UK) address - 1 Abbey Rd, Watchet and put a waypoint there. The coordinates should be roughly 51.159537, -3.364398
If you then open that route in the mobile app the waypoint has moved to the right (and in fact is in a river). If you correct the waypoint in the mobile app, then re-check in the web app, it has moved into the building on the other side of the road.
If you can't reproduce the problem let me know and I can send you something.
Sorry for the delayed response. There appears to be a very slight difference in map version that results in the waypoint for these coordinates being displayed next to the road in the app, and on the road online. This should automatically be fixed within a few weeks, once the maps are updated. It does not affect calculation, because the same coordinates are used online and in the app. Furthermore, the visible difference seems to be limited to ~50cm so this should not create any major problems. In case you do expect problems, just make sure to place the waypoints in the middle of the road.