I ran into a very strange problem.
I need to manually initialize the Vuforia engine and create the AreaTarger at some point.
I created a test scene with three buttons, which are to load the AR scene (only one AR camera), initialize the AR engine, and create an AreaTarget.
The target status: TRACKED status can be obtained in the test scenario.
The same process, when I put it in the project scene, it will report an error, "ObserverNotCreatedException`1: Failed to create AreaTargetObserver: TARGET_NOT_FOUND.".