Hello Ruby Triplett.
I am not the writer of this post, but I was directed to here by a friend, because I am having the exact same issue shown in this post. I saw that you wanted to reproduce the issue in a clean project, and to provide a detailed list of steps to reproduce the issue.
I’m writing you this message because i’ve run into the same problem, and can reproduce this issue easily. I can also show you, very easily, how to make a set up that will demonstrate this issue.
I was following this UE4 tutorial. https://docs.unrealengine.com/latest/INT/Videos/PLZlv_N0_O1gYeJX3xX44yzOb7_kTS7FPM/aqRUe7pm4Ok/index.html
Once I was finished everything worked fine, except for the boxes that I made to fall onto my conveyer belt. They would land on it, but they would move along the conveyor belt at all. regularly placed items would move with out any issue, it was only my blueprint items.
I went through the tutorial, and made sure I had every thing set up just like him, to no prevail.
After tinkering with it for a bit, I found that once I took my cube inside my blueprint, and took it out of the DefaultSceneRoot, witch basically deleted the DefaultSceneRoot, the problem was fixed instantly.
I feel very confident , that if you use UE4 version 4.11.2, the version i was using, or later. You will have this same issue.
If you have time, I would really appreciate it if you could go through that tutorial when you have a chance, and see if the same issue happens to you. If it does, I would really appreciate it if you could explain to me why it happens, or let the team a UE4 know that this is an issue :).
Thank you very much for your time, and I hope to hear from you at the earliest convenience :).