Could not save some Folder to Optimize

Hi,

First I would like to thank you for your amazing plugin that I install on almost all website I develop.

I Have a little problem on one of my websites (I have an API key)… I wanted to add several custom folders to be optimized but for some of them I got the error : “Could not save Folder to Optimize…”

I have been able to add the following folder :
/var/www/html/web/app/uploads/fv-gravatar-cache/

but I couldn’t add these ones :
/var/www/html/web/Images/
/var/www/html/web/app/themes/assets/images/

these 3 folders have www-data:www-data ownership and 755 permission. Do you have any ideas why these 2 folders are being rejected ?

thank you in advance for your help

The page I need help with: [log in to see the link]