Since the Earth is a sphere, the elevation of the track must be adjusted manually in "Google 3D" mode.
Once the GPX file is loaded, you'll see the red line, or if it's too low, you won't see it. You can adjust the elevation of the GPX line using the "H" and "G" keys. Once you've adjusted the elevation, you can hide the line using the "L" key. If a lateral offset is required for the rider, this can be fine-tuned using the right/left arrow keys. The camera can be adjusted as usual using Page Down/Page Down and the up/down arrow keys, but this time you don't need to press the key repeatedly; simply hold the key until the desired position is reached.
This means you can now ride anywhere in the world without jitter.