Optical flow, OpenCv and updating FBO?

Hi! I wonder if someone could give their insights on these results using optical flow.

I have a 3D shape that has an FBO wrapped around it as a texture. The contents of the FBO vary every now and then: some of the contents are images as ofTextures and one content is live video feed from vidGrabber. With ML and classification, this has worked so that sometimes I can see my own face in the shape, sometimes an image of a mammoth and so on. I have followed code examples from this book: "openFrameworks Essentials" book has been published

However, with optical flow, results are very different. Optical flow tracks my movement and affects the 3D shape. Now, each image (or video) only shows some colors, not content in more detail. I attach here a picture that shows how the video is like (that’s maybe my face or hand in the screenshot).

I suspect that optical flow somehow occupies my video feed: that because it is used for motion tracking there is some problem with updating the video. However, my other FBO contents are affected in the same way: showing only blue instead of the actual image ofTexture that contains a piece of blue sky etc. Is this familiar to anyone? Warm thanks!