Weird optical flow output w.r.t. older implementations of NVOF

I used the NVIDIA Optical Flow SDK almost an year ago with great satisfaction. Some days ago I got access to a new machine equipped with an RTX 3080 GPU and I decided to try the new version 2.0 using latest OpenCV.

However, it seems that the performance, at least for my scenario, became worst.

Given a frame with static background and a moving object (held by a person whose arm is part of the scene), the output of the NVOF 1.0 one year ago on a mobile RTX 2080 was the following:

Instead, using the new RTX 3080 and latest OpenCV and NVIDIA drivers I am getting totally different result.

This is the output of the NVIDIA Optical Flow 1.0 on the new configuration

and this is the output when using version 2.0 with per-pixel precision

While the flow associated to the object seems right, the static background that was almost white in the past now is full of non-zero flow vectors (even with huge magnitudes).

How is it possible? Can I do something to get back the old results (that were looking much better to me)?