White thumbnail when sharing to facebook

Hi. I’m having the following problem : when i want to share the link of my blog ( https://blog.gm-shop.ro ) to facebook, i have only 1 thumbnail, which is white. What can i do to fix that ? Before this, the thumbnail were take from the last posted thing, or maybe some older. I tried the facebook debugger and told me nothing …

Link : https://blog.gm-shop.ro

Thanks !