Hello @bredamcguigan
This is most probably happening due to two reasons:
1. Smush is compressing only the thumbnail versions of an image, not the full-size image. If you’re using full-size images in your homepage, you should compress them too. Free Smush doesn’t have that option, you should first acquire a WPMUDEV membership which will let you use Smush Pro instead (apart from the other plugins and services we offer), which include a “Smush my original full-size images” option.
2. Images used in homepage, are much larger than their containers. So if an image is loaded that’s for example 500*500px and it’s getting shrinked via CSS in a container that’s 200*200px, Google will moan that you’re loading unnecessary large images. Smush can’t do anything about that, you should either contact theme author or resize/crop your images via native WP image editor. More info: https://premium.wpmudev.org/blog/compress-resize-images-wordpress/
In order to find out, which images are getting reported, just click on the “Improve” button in Performance Report of HummingBird.
If the reported images are mentioning that need “resizing“, then it’s case #2 from above.
If they only state that need “compressing” and there’s no thumbnails sizes in the end of the filenames, then it’s case #1.
Hope that was some help!
Warm regards,
Dimitris