Assertion failed and transform.localPosition assign attempt for 'BackgroundPlane' is not valid error

Hi guys ,
I'm developing an AR application in which camera is actually made into a box of a particular width and height, instead of laying it full screen. The application has two screens in which first is for logging in and the second is the one which has the ARcamera(Vuforia). after logging in the second scene would be loaded but while logging out from the second screen first scene would be loaded on top of the second screen.

I tried using the LoadSceneMode.single but no use, the second scene keeps coming under the first while logging out.

Im actually very much new to the unity and AR development, So a help would be well appreciated.

And also having the following errors

• transform.localPosition assign attempt for 'BackgroundPlane' is not valid. Input localPosition is { NaN, NaN, NaN }.
• Assertion failed: Assertion failed on expression: 'IsMatrixValid(matrix)'UnityEngine.Camera:set_projectionMatrix(Matrix4x4)Vuforia.MonoCameraConfiguration

These errors are not present when the Camera is fully layed over the screen, i dont know if the above errors causes the other issue as well. Please help