Diff Pair Nets are displaying errors when necked down

We are using a diff pair with the default gap at 15thou and 15thou width, but we also have the necked trace and gap set at 6thou.

When routing, the 15th is fine but when we route to a fine pitch IC and attempt to neck down the traces, we get a width and spacing error appear. It is as if the necked traces are not working.

Any suggestions? We are running 16.6.