Error while Annotating Semantic Segmentation Images

  1. Project type (Semantic Segmentation using Polygon)
  2. I use the basic version, which is available for free at Roboflow

I have annotated some images and at the end
I tried to export the semantic segmentation annotated images and the original images, having two options: 1. download the zip file and 2. use the code on Google colab.

The same problem occurs with both variants. The original image (png format) can be seen, but the mask (with semantic segmentation) is completely black. What is the reason for this? What am I doing wrong?