Ambient Occlusion (AO) maps stopped working in one scene.

As the title says, yesterday the AO maps worked fine, today they don’t work at all.
If I start a new scene and drag in the same objects with the same maps - they work.

What could be stopping ao maps from working in a scene? Is there some setting I may have changed without realising?

@MikeErty I’m having the same problem. I specialize in low poly optimization, and all the features of Physically Based shaders let me obscure a lot of lack of actual detail by using texture data. Occlusion maps used to help too but now they do absolutely nothing at all. My content creation workflow relies on the ability to create materials with 0% diffuse amount areas, ie. places where the albedo reflects no light.

My problem actually extends to the entire editor. Regardless of which scene I load or create from scratch, occlusion maps have no effect on visuals.

Just my luck. Baked and dynamic lighting mix is finally starting to work properly, and now PB materials are breaking down.