Plane to Plane Transition Need help!

I am a newcomer to Unity. I have completed the Roll-a-Ball tutorial and am expanding on this for practice. However I have encountered a problem when the player transitions from plane to plane.
For some reason with my 2 planes scaled and positioned exactly the same on the Y axis there is a "bump"
in the transition area when the ball rolls over the joining section. Can anybody give me some pointers here or explain to me why this happens. I can present the file for inspection if needed.

This is also my first post on the forum so if it is in the wrong location I apologize in advance.