Compare to Part Structure not available (grayed out)

I've got a Creo CAD assembly in Windchill that is linked to a WTPart using the Owner link. The part structure will successfully build. The problem is that for some reason on the CAD page, the "compare to part structure" button is grayed out. On the WTPart page, I am able to get the comparison.

I've checked for failed placements, and that doesn't seem to be the issue as the structure will successfully build. I've tried unassociating the WTPart and reassociating it. I've tried checking out the CAD model regenerating, saving, and checking back in. I've even tried suppressing everything and then checking back in. The compare button continues to be grayed out. 

Any ideas how to resolve?