Have used Garmin GPS units for 20 years and over that time frame have learned a couple of things:
1) When you plan a route with waypoints or just successive points on the roads when you are done. ZOOM WAY IN on the route and verify that each and every point is ON THE ROAD, not in an adjacent parking lot or field. If the point is off the road, move it onto the road while zoomed way in. That will solve your waypoint issue. Note for auto navigating, this applies to INTERSTATE HIGHWAYS, be sure your point is on the CORRECT side of the road for your desired direction of travel.
2) If designing a route on your computer and copying to a device, BE SURE the maps on each are the same version. Otherwise the computer and the Garmin MIGHT calculate different routes.
3) Sharing of routes from one Garmin to the next is technically tricky. A route is transferred to the Garmin unit as a series of points. First, I found even TWO IDENTICAL models might recalculate the route differently. Why the difference: through trial and error: A) map version is different, B) software version is different, C) data sets for roads that connect or even points on the same road are different.
4) These situations are even more complicated between different Garmin models and even worse between different GPS brands.
HTH