Facebook thumbnail missing

Hi, I’ve noticed that FB doesn’t generate a thumbnail when I link my home page. Individual posts seem to work fine – it picks up images embedded in them as thumbnails, but not the home page URL.

I requested FB to scrape my site again using the debugger (https://developers.facebook.com/tools/debug/sharing) with no luck.

Any idea how to fix this?

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