I have found some things that help me.
If I have a route that I download from MapSourse I remove the start point (home), it may want to send me home just after I leave.
I don't make round trip routes anymore. I make at least one route for each direction, maybe more.
Make sure your GPS is set the same as you routes from MapSourse., like "quickest" "shortest" and the things to avoid.
The last time that I did a round trip route I also took a new section of highway that just opened, that really messed the GPS up. After that I just used "go to" the next waypoint for the rest of the day.
Most of the time I am on roads I know so it is not a problem if the GPS wants to take me another way.
If I am on unfamiliar roads I don't know that it took me out of the way.