Rooms not showing in CAD input following DXF update


I've got an existing Hevacomp model which works fine in CAD input.

But I need to update the DXFs and change a couple of zones.  When I bring in the new DXF all the CAD rooms on the floor disappear.  The rooms are still there, because they show up in the 3D view and and I can bring them up using 'find room'.  However, when I do this, the DXF disappears form the view.

Is there any way of correcting this?

DXFs are lined up with the previous DXFs, and set to the same scale.

I've tried clearing the chache of the old DXF links, but this hasn't fixed the problem.

DXFs have different names to those used previously.  But there is no way of avoiding this, because previously one DXF was used for multiple floors.  Now, each floor is different and so needs a different DXF for tracing.

Any help will be gratefully received.