Unity 5.6.1 and vuforia 6.2.6 reloading AR scene issue

I have 3 non-AR scenes and 1 AR scene in my application. i noticed that when i switch between the scenes for 2-3 times, the AR camera does not load the background plane with the webcam texture. It keeps showing the camera video background texture. But when i reload the app from the beginning by closing it, it works fine but not more than 2 times. I see that the webcam is initialized but the webcam texture has not been applied. please refer to the screenshot from the editor. it keeps happening on the app as well.