I tried reproducing this off the steps you’ve given but it appears to move for me without any issues. Here are some screenshots to be sure I’m understanding you correctly.
Are there any other specifiers you’re using when creating your UPROPERTY or for the class itself?
That doesn’t make any difference for me. Are you ensuring that you’re selecting the diamond itself instead of the SceneComponent or the root of your actor? I accidentally didn’t do so when first testing this and it seemed like what you’re describing.