That is odd. Maybe the shadow atlas resolution is low?
Do you see any issues with the example project that comes with it? It has high resolution assets which should look correct.
Does it happen in every room too? I've often seen that once you use the in-room camera or viewports it does something that causes conflicts. Its very odd, but if you can try in a fresh project and use only a camera made through code.
If you need, get my camera manager here free: https://github.com/badwrongg/gm_camera_and_views
Get the yyz project file and import it. Then create a new local asset from it that you can reuse in any project. Using that camera should have no problems.