Rendu carré gris / Render missing gray block

If the render is complete but missing square blocks this is usually a 'bucket failure'.  The rendering and denoising happens in chunks called buckets, and one of those failed to process.  To temporarily fix the issue just disable the denoiser in the render settings or try a different combination of render settings (the bug may be at a higher sample rate, for example). 

The only way we can fix the issue permanantly is to have the scene that caused the issue.  If you're able to share your saved SSG scene with us (you can email to us at Substance3DBugs@adobe.com)