You are using layers incorrectly. Layer 0 should be active at all times. Faces and edges should remain on Layer 0. Only groups and components should get other layer assignments.
There’s no face in that region to add to your group but if you open the group for editing, you can trace the region you want to add and it will be included.
There is a face that includes it but you have it included in a different group that has the layer visibility turned off. It’s the face shown in magenta here:
I really tried, and managed it with the first lot of groupings, but as I started needing to copy groups to be able to get different floor levels it all started going pear shape.