Replacing an Image with another one

In the WordPress page editor, when i click once on an image in visual mode, then click on the popover edit icon, the image details window cover the screen.

75% of the time, there is a button ‘REPLACE’ to replace the image with another one, and 25% of the time that option isn’t there.

Is there something I’m missing or not understanding? Why is the button “replace” missing some times?