In the unity we place the 3d object 0,0,0 position which is directly above the marker also positioned 0,0,0 but when in play mode and even in phone after exported to apk, the 3d object is way above the marker.
Placing an object at (0,0,0) is not (per se) a guarantee that the 3D model will appear well centered on the Target; this depends on where the actual original (center) of the 3D model is located with respect to its actual geometry (you need to check this when you export the 3D model from your 3D editing / modeling tools);
from a Vuforia point of view, you can verify that the centering is correct using a simple a 3D game object like a Cube or a Sphere (see also the Image Targets sample app).
Also, when the marker is detected, the UI in the exported apk becomes white and there are some angles where in the screen went white but after we take the camera out of the marker the white disappears. I will post screenshots after this.
This is probably because you are using an old version of Unity 5.0 or 5.1;
if you are using Unity 5.0, the recommended version is 5.0.3 or newer (versions 5.0.1 and 5.0.2 are affected by the white UI issue you describe).
If you are using Unity 5.1, the recommended version is 5.1.1 or newer (5.1.0 is affected by some UI rendering issues, similarly to 5.0.1 and 5.0.2).