When background image is not found, the image button doesn’t allow to replace it.
In the bricks panel it only show a message “Image not found”, in previous versions when this happen, you cant change the image size and then the control to replace image was shown.
I’m leaning towards marking this as a no-bug, because you can always clear the field with the yellow indicator. But, I’m wondering how to replicate this - I tried with non-existing custom URL, but I guess you got to this differently?
Because for the URL, I had the option to update the path.