That is a classic image of a route that is created outside of BaseCamp / Mapsource where some of the waypoints * / shaping points are off the road.
The main cause of them being off the road is the difference between whatever maps MyRoute uses (maybe Google maps, I guess) and Garmin’s own generic mapping.
The Garmin device then does its best by routing you off the road into what is maybe a field, up to the point and back out again. I can create the same effect
deliberately in BaseCamp by placing a point off the road. Other than rarely, I don’t get it by accident as I never stray from Garmin software and always try to check that the shaping points / waypoints are on the carriageway.... unless of course I want the route to go off the carriageway, into a road for example that is no shown on the Garmin map. Then I get the straight line. When creating a route in BaseCamp on a Mac I get a telltale warning that I have placed a point off the carriage way, as the point appears as a number in the list. If I get one, I go back a stage (edit) zoom in and place the point correctly.
See this thread from post #7 onwards, as the spikes and bizarre routing look very similar:
https://www.ukgser.com/forums/showthread.php/510280-Garmin-396LM
PS If, as in the post linked above, you share the problem route with us, it may save some time.
* I suspect they are waypoints (points you have told the device you MUST go through) which might explain the circular loop, when the poor dumb machine tries its best to take you into fields and back through a must do point that is then behind on the route.