Thank you for reporting this issue. Sorry to see this is affecting your usage of Roto Brush 2. We aren't able to reproduce the same issue on our machines here with a new project and test footage. Would you be able to share a project with us that is exhibiting the issue? Footage should not be required.
I do note that the Paint palette shows the current color as red while drawing with the Roto Brush tool appears to draw black or possibly erase the layer. Do other tools in the