UV Texture animation help

I’m following a tutorial about UV texture animation and I can’t get it to work. I’ve tried 5-6 times. I just don’t know what I’m missing.

animate_texture_not_working.blend (530 KB)

EDIT: JPG works without problem, but PNG doesn’t. What more does the PNG need for it to work?
By the way, I don’t want to place duplicate planes on the scene and animate them. Nor do I want to use addons. I want to get things working with the built-in default Blender functionality.