ball's collider sometimes catches an edge and bounces. when ball rolls over two aligned platforms

If the platforms are rectangular, you may be able to add a (or resize an existing) box collider to one of the platforms, and resize and reposition the box collider to cover both platforms. If both the platforms already have a box collider (that's not a trigger), you can instead add a plane (or really thin cube) just over the top of both platforms. Remember to remove or disable the renders if adding a new cube or plane. - something also came to mind...If your platforms aren't using static colliders and/or rigidbody on the platforms isn't kinematic, one of the platforms may actually be moving, but I'm guessing that both platforms have static colliders already. Next thing to check would be to ensure they're both using the same physics material.