here is what I am experiencing, it worked one time then suddenly went back to doing this again.
https://drive.google.com/file/d/1GtoVpq3FI-4CqB-QLJbwZgcR14Pw275n/view?usp=sharing
After you pick a Test file and the preview window opens to show you the image, close that preview window. Do the same after you open the Reference image.