Are the optimized images displayed right away?
Once you turn on the option to optimize images in Autoptimize plugin
you or your visitors will need to access a page before the images on that page are optimized and served from the CDN.
Basically unless a page is visited, the images on that page won't be optimized. This is good as your website won't use more resources than needed at once. The flip side to this is that the first user visiting a page won't see any speed improvement at first.