Catch Everest Facebook Thumbnail

On some of my posts and pages you click on share on Facebook and it pops up with a selection of thumbnails, as it should. On other posts and pages it either shows no thumbnail or on a couple of pages it opens another page of my website and doesn’t connect to facebook at all.

I was told to run this: https://developers.facebook.com/tools/debug which I have. It says:
Open Graph Warnings That Should Be Fixed
Inferred Property:
The ‘og:image’ property should be explicitly provided, even if a value can be inferred from other tags.

I have NO idea what any of that means.

I like the look of this theme but it just seems I fix one thing and then something else needs to be fixed. I’m never going to have time to write, I’m fulltime fixing the website!

Please help!!! Tanja https://www.tanjacrouch.com