This happens when the tracker is unable to get a correct GPS position, in a garage for example.
Do not worry. Your vehicle is still protected in case of theft: Trackting SMART will alert you immediately and provide an updated location as soon as it locks on to the GPS satellite signal again.
The reason it works this way in "Parking" mode is to avoid all unnecessary battery consumption. Therefore, if the device fails to get the correct GPS position in just a few seconds, it goes back to standby mode.
In "Alarm" mode, the goal is very different: we want to read valid positions as soon as possible. This is why the tracker stays on when your vehicle moves, up until it gets a valid GPS position.
N.B. On some motorcycles or mopeds with an all-metal body, as in vintage models, it is important to avoid placing the Tracker in a completely closed compartment: operation may be affected by not correctly locking the GPS signal.