Webp Express & my own htaccess

This plugin is great, thank you.

I’m trying to protect some uploaded images with this htaccess:

<FilesMatch "\.(jpg|jpeg)$">
    RewriteEngine On
    RewriteCond %{REQUEST_URI} !.*/[^/]+-[0-9]+x[0-9]+\.(jpg|jpeg)$ [NC]
    RewriteRule . - [R=404,L]
</FilesMatch>

I use this in wp-content/uploads/…

Works fine, it shows only images, which meet the rules (like image-100×100.jpg, image-100×150.jpg etc.), for the others (like image.jpg) returns 404.

But, with this htaccess Webp Express is not creating ANY new files (like image-100×100.jpg.webp, image-100×150.jpg.webp etc.. Any idea, how to solve it?

Thank you very much.