This is an interesting case. Enscape will determine automatically what edges to paint outlines on and what not. For this, it takes into account aspects like scale, distance and angle.
An angle of 90°, as it appears to be in your case, should render an outline just fine. The first thing that comes to my mind is that maybe your model scale overall is very very small? Could you scale it up to check?
If that’s not the root of the issue, can you please send us the model for inspection to support@enscape3d.com? We’ll be happy to look into it.