So I make a new screenshot for this url:
https://www.glansbeton.be/projecten/
Please check the source. Al the needed og: tags are in this URL
<meta property=og:locale content=nl_NL><meta property=og:title content=PROJECTEN><meta property=og:description content="glansbeton industrievloeren en woonbeton"><meta property=og:type content=article><meta property=og:url content=https://www.glansbeton.be/projecten><meta property=og:image content=https://www.glansbeton.be/media/k2/items/cache/47e29f9fe96a1771642fb05ac8a8fd00_L.jpg><meta property=og:image:width content=1200><meta property=og:image:height content=675><meta property=og:image:secure_url content=https://www.glansbeton.be/media/k2/items/cache/47e29f9fe96a1771642fb05ac8a8fd00_L.jpg><meta property=og:site_name content="Glansbeton Industrievloeren en woonbeton"><meta property=fb:app_id content=842361175883763><meta name=twitter:card content=summary_large_image><meta name=twitter:site content=@glansbeton><meta name=twitter:creator content=@glansbeton><meta name=twitter:title content=PROJECTEN><meta name=twitter:description content="glansbeton industrievloeren en woonbeton"><meta name=twitter:url content=https://www.glansbeton.be/projecten><meta name=twitter:image content=https://www.glansbeton.be/media/k2/items/cache/47e29f9fe96a1771642fb05ac8a8fd00_L.jpg>
Start to type in joomsocial website, no image! https://prnt.sc/ytnbo4
Post on the website --> https://prnt.sc/ytnyo2
Please check you're self on the website --> https://www.offirent.be/stwg3
I don't know what og:tag there has to be on the website more. But I have no control on other websites, the same like facebook twitter has no controll over websites from other webmasters.
Checked on the facebook debug tool:
https://developers.facebook.com/tools/debug/?q=https%3A%2F%2Fwww.glansbeton.be%2Fprojecten%2F
The thing is just with facebook and twitter there is a good image. This is one of the most important features of a social website I guess.