If I am understanding your scenario, this is the expected behavior.
For your mobile to unlock your Lucid, the following must be true:
- Your phone has Bluetooth on
- Your Lucid app is Running, either in the foreground (like it's open and you're looking at it) or in the background (the app is not open but it is running).
When both are true, your car will unlock as you approach with your mobile.
So, now you may be wondering about #2 and what's the difference between "background" and "app not running at all".
- Well, on Android once you open the app, even if you switch to another app, the Lucid app is still running (and so the Mobile Key will continue to function). If you view all of your running apps (hit the square on the bottom or swipe to show square, dot, and back arrow on the wallpaper), you can see all your background running apps. If you swipe up on any app, the app will close (e.g. it will not satisfy #2). You can of course stop the app by using the Settings-->Apps-->Lucid-->Force stop.
- On iPhone you will want to lookup whether apps run in the background and optionally how to stop them
So, the reason it worked for you once you opened the Lucid app is because it was not running (foreground, nor background). When the app is not running, it will not unlock the Lucid.
See also:
https://lucidowners.com/threads/mobile-key-unlock-without-knowing.6074/post-143505
Hope that helps