Src not updated in img tag, but updates the srcset

So this is what this plugin outputs, as you can see it didn’t update the src in the img tag, just the srcset.

<img class="wp-image-1929 size-medium aligncenter"
     src="https://www.xxx.me.uk/wp-content/uploads/xxx-500x333.jpg"
     alt="Fleet Prison Marriages" width="500" height="333"
     srcset="/wp-content/uploads/xxx.jpg 500w, /wp-content/uploads/xxx.jpg 768w, /wp-content/uploads/xxx.jpg 1024w"
     sizes="(max-width: 500px) 100vw, 500px"/>