The problem: PageSpeed Insights says images aren't being lazy loaded and the documentation says the img tag should be replaced with "data-pagespeed-lazy-src" attribute (its not doing that).
pagespeed.conf:
...
ModPagespeedEnableFilters lazyload_images
..
HTML rendered:
<img width="100%" height="100%" src="/img/xstrategy_creation.png.pagespeed.ic.3BVepnuhcw.webp" data-pagespeed-url-hash="3308235655" onload="pagespeed.CriticalImages.checkImageForCriticality(this);">
It's converting the png image and I see the "X-Mod-Pagespeed" header so I'm sure the module is there.
/pagespeed_admin shows that "Lazyload Images" filter is enabled. The onload javascript resource also looks like its attaching.
It seems like its half working (attaching the javascript onload to detect if the image is above the fold). I tried refreshing the page a bunch and giving it time, nothing ever changes. Image is below the fold.
I've purged the cache and still get this result.
Even the example given by pagespeed documentation doesn't seem to work: https://www.modpagespeed.com/examples/lazyload_images.html?ModPagespeed=on&ModPagespeedFilters=lazyload_images