One way for this to happen is for the VI to be saved on a different platform (Mac / Linux / Windows). If you open a VI on a different platform from the one it was compiled on, its object code is tossed. If that VI is saved in that state, the object code is removed from the file.
Normal (non-CIN) VIs are recompiled as needed. But CINs need external object files for the platform they're being compiled on.