If you have an actor in a folder in the Scene Outliner, and the folder is collapsed, alt-dragging the actor to create a duplicate will result in moving the new actor one grid unit, and then losing the selection.
To repro, create a new map, add an actor, create a new folder for that actor and collapse the folder. Alt-drag the asset and notice you lose the selection after moving one grid unit. Now expand the folder so the actor is visible in the UI, alt-drag, and notice it works as intended. Tested with static meshes and lights.