Just to be sure, you got this result with the car plugged in? When unplugged, the battery will drain (from a full charge) within ~5 days if the car hasn’t been powered off using the Turn Off button in the settings screen of the app, so it could have been powered off if it was unplugged at the time of this test. If the car is in “sleep” mode and you plug in the charger, the headlights will not normally turn on until the app connects.
If it was plugged in, then something is wrong either with the car, the app, or the phone. An interrupted firmware update shouldn’t prevent the app from detecting the car. If you still get the message about not being able to find Lightning after reinstallation or from other phones or tablets, with the charger connected, you should contact customer support by emailing email@example.com.