I am such a newb...

I really hate to ask, but this has been killing me. I have been trying to make the AR ball maze puzzle game in this tutorial

, but have been having no luck getting ANYTHING to work. I have had every unanswered issue in the video's comments (ball flickers and doesn't drop, ball continuously falls and respawns, ball doesn't show up at all, etc.) I've searched all over the net and tried the tricks that I found but still nothing. I have pretty recent Unity and Vuforia, and the video is from three years ago - the interfaces are different but I think I have found and followed/updated the instructions in the video to work in the newer versions, but I don't even know if that'd be the issue.
To trouble check, I have started a project with nothing but an AR camera, a target image, a plane and a sphere with colliders (no respawn script yet, just want to see if I can get the ball to fall onto the plane once at this point) just to start from scratch. I'll build it to my phone to test and the plane and sphere show up, but then when I go back and add gravity to the sphere, when I build it to my phone the ball is no longer there - not flickering, not dropping off into the distance below the plane, just gone. I have tried the mesh plane with both box and Mesh Colliders, tried moving the target image and plane and sphere farther from the AR camera. I know that making games in Unity has a intense learning curve, but I would assume that this project would be an easy first step and I'd really like to just make the game and have it work.
If anybody has any advice that they can give I'd certainly appreciate it. I am continuing to try to get the gravity to work, but I will soon run into getting the ball to roll on the plane as the target tilts, and I have already run into issues there the one time I got the ball to fall - it wouldn't roll and just stuck to the center of the plane (don't ask me what I did that time to get that far, I immediately lost that as soon as I tried to address to not rolling).
Anyway thanks everybody - if you've built this and have any insight I'd appreciate any advice you can give.

 

No thoughts?