Latest update 1.4.8 broke W3C validation

fwiw, this is as intended. See https://github.com/verlok/lazyload/issues/211#issuecomment-397795568 and https://github.com/verlok/lazyload/issues/89 and

https://github.com/verlok/lazyload#do-not-use-placeholder-images

verlok/lazyload is what is used under the hood by this wp plugin.

It’s safe not to put any value in the src nor srcset attributes, even if your HTML won’t validate by a static code analyzer. The reason is that once JavaScript is executed, those values will be set by LazyLoad. For SEO, if the client is a crawler like Googlebot, it will be detected by LazyLoad which will fix the HTML.

So you can ignore these “errors”. Or even better do not use a static validator but run tests in headless Firefox or headless Chrome.

Disclaimer: Just a user, not plugin author.

The first item is fixed in 1.4.9.

For the second, as commented, it’s on purpose to improve performance