I know this issue pops up periodically. But I still haven't found a solution. The problem is on this picture.
Other projects render great even with 128-64 samples. I realized that the problem is not with samples at all. I tried big numbers, but it's useless. I was thinking about denoiser, but: denoiser off - it gives awful noise; OptiX gives this result; openimagedenoise gives smth like this but worse.
Few hours ago everything was good. The project rendered without any problem. Well, I created a couple of shape changing objects. But logically they can't increase the noise. In addition, I tried to render without them. The same result.