I get asked a few questions about how to plot routes and transfer them to Garmins, so I wrote a couple of blogs on the subject
However, the problem I’ve noticed most with routing is caused by the same “feature” that people inadvertently have enabled. If you think about a car satnav you tend to put in a destination and then follow the route the device calculates for you. If you take a wrong turning you rely on the device to recalculate the route and still take you to your destination. The default behaviour for Garmin bike satnavs is to do that too. However, if you plot a circular route where you start and finish from the same spot, that doesn’t really work, because as soon as you go off-route your Garmin will calculate the quickest route back to the start.
So if your main use for your Garmin is based on circular routes you plot yourself then make sure you set this option (found in the routing or navigation options menu) to either off or prompted. If you set to prompted you will be given a dialogue box if you go off-course. If you do not select NO then it will timeout and default to recalculating.
Hope this helps