An Instanced Static Mesh Component can only have 1 Static Mesh:
It can then instantiate that one mesh many times, and very efficiently, too!
If you wanted to have 1 trap (we’re making traps, right?) with many different spikes and still use ISMCs, you’d need more than component.
So you’d need 4 ISMCs, each with a random spike mesh and then let each ISMC instantiate its own spike Static Mesh. Or use many Static Meshes instead which can be added dynamically.
At the moment it seems that you’re attempting to have 1 ISMC have various meshes assigned, that’s not going to happen. Perhaps you could tell us more about the spike actor you’re designing - we might be able to push you in the right direction.