The most common GPS Follow Me confusion: the drone follows the controller, not your body. If you are mountain biking and your controller is clipped to your handlebars, the drone tracks your handlebars — generally fine. But if someone else is holding the controller, the drone follows them, not you.
Controller placement affects GPS signal quality. Putting the RC in a jersey pocket pointing down partially blocks the GPS antenna, degrading tracking accuracy. For best GPS follow me performance, mount the controller high on a chest or handlebar mount with the antenna facing upward so it has clear sky view.
Some DJI drones support Follow Me via the RC controller's GPS directly, while others use the DJI Fly app on a phone. Phone GPS is typically less accurate than a dedicated controller, and phone GPS updates slower (1Hz) vs controllers (5-10Hz), which makes the follow motion jerkier at cycling speeds.