Facebook uses cache so changes are not immediately seen.
Facebook Debugger says "
Provided og:image, thegamerslife.eu/gamers/media/k2/items/cache/e17bf28887a04e7713039bc3ae638d41_XL.jpg could not be downloaded because it exceeded the maximum allowed sized of 8Mb or your server was too slow to respond."

So you need to use a smaller image size.
You can check your og: tags here developers.facebook.com/tools/debug/sharing/?q=http%3A%2F%2Fthegamerslife.eu%2Fgamers%2Ftemplate%2Fk2%2Fk2-categories%2Fnews%2Fitem%2F282-overwatch-new-map

I've now come to realise, what is happening. Everytime I make an article, it doesn't respond properly in order to generate the thumbnail. In all occasions, 2 days after the creation of the article, the thumbnail magicaly generates. I really do not know why

Do the following:

- Remove the extra code.

- Ask the template's dev if there is extra code which generates og:images (probably not)

- In K2's settings, select a smaller size for the og:images.
The setting is called "Image size to use when posting K2 items on Facebook", you should select Medium.

- Wait a few hours until Facebook's cache clears and the changes can be seen ( we have no control over this ).

This is default functionality and it works out of the box without the need to put extra code.