Wake Rigid Body not waking a rigid body?

I have a forklift blueprint. it has a skeletal mesh (not scene root), to which I have added the fork as a static mesh component, which I drive up and down with setrelativelocation.

Lifting and lowering pickups in my level work just fine, but if I drive backwards away from the thing, it remains floating in the air - and nothing can move it. I have tried to force wake rigid body on the mesh - nothing changes.

Sometimes the forklift will bump into an invisible collision box nearby the mesh. it’s almost as if they get disconnected somehow.

Anyone have any ideas how to solve this - or what could be causing it?

Thanks