I am having a strange problem. I installed V-Ray 6 and had issues with Forest Pro, so I uninstalled it and reinstalled V-Ray 5. I was working on an interior, which I don’t do much of, and I couldn’t get past the noise issues. I didn’t think it was a software issue, so I shelved it and went to work on an exterior, which I do hundreds of. Now, the exterior is having the same noise issues. One hour of render is always enough with Denoiser at .4 in the layers. Now, even setting the denoiser to 1 and two hours later, the noise is so bad the image isn’t usable. So what happens when you install 6, remove it, and install 5? Is there something left behind that would cause this? I can toggle the denoiser off/on and see that it is working, but not good enough. On the interior, the progress seemed to stop working altogether, and the VFB stopped getting cleaner.
I can’t say what’s exactly causing this. But if you are working on the same file, it is always good idea for such cases to reset render settings by changing the renderer from VRay to something else like Corona then back to Vray to make sure there is no any left over from the other version.
Yes, that is usually the first thing I do.