Hello, so ShowRoute isn't actually supposed to be a tool for navigation, which doesn't currently exist at all in this widget. ShowRoute is supposed to show the locations over time so you can track things. I am not sure exactly why they are appearing as straight lines, but I do know that this isn't the purpose of ShowRoute. Because the locations aren't actually related to one person traversing a route, then that is probably why it appears funky.
If you think that ThingWorx should add navigation route functionality to the widget or if you want a real explanation of what you're seeing, I'd try opening a case and attaching an entity export for review.
Hope this helps!