By disabling select2 the image of the variable is shown … but still impossible to add more, as I had understood with your sentence “Add attribute images of a variable product on its own gallery”.
The color choice as type is not displayed correctly, the column of terms is compressed in width. see https://madeit.ch/wordpress/wp-content/uploads/2018/01/capture_problem_color.png
“Displays only the possible term combinations” does not work, it was also one of the main reasons for my purchase …