You got this warning (or something similar):

What's happened?

The building has too much articulation around the facade or tightly angled edges which have caused problems for the perimeter-core zoning algorithm.

Rather than crashing your model we've automatically reverted the floor to a single-zone per floor model.

How can I fix this?

First step is to try reducing the perimeter depth here:

If that doesn't work and you still want perimeter zones there are 2 options:

- try drawing perimeter zones by hand in your model and use the one zone per room setting 

- try flattening out the articulations on the facade (narrow spaces, pointy edges, narrow abutments).