I had a similar issue with some of the posts where the ball would fall, but when it made contact with the floor, it would no longer move with the movement of the platform. I saw a few posts here that were resolved, but I wasn’t able to duplicate their results. Here’s what solved it for me.
I selected the ball, and under the actor panel, I changed the Spawn Collision Handle to Default. My ball was set as Always Spawn, Ignore Collisions when I created it.