Open this file in Studio. Note that all the Cactus MeshParts are selectable in studio, and have Can Collide set.
Select the Ground part, and select the Cactus folder, and copy.
Open a new Baseplate project in Studio. Select the Workplace, and Paste into. Now note that in Studio you cannot select any of the Cactus MeshParts (except for one). Also note that when you hit Play, that you can walk right through the MeshParts, even though Can Collide is set.
So, it seems like the collision box is lost upon copying and pasting.