Thumbnail not shown in RSS and when shared on FB

Hi,
I dont know what to do anymore, have been searching a lot but nothing works.
Since May, I have been facing issue with no thumbnail shown in some RSS feeds (https://www.blogerky.cz/blogy/vareni/1001-voyages-gourmands) and when shared to FB (only frame with a blog url shows, not even the meta description! and I use Yoast SEO where I fill the meta desc., add an image for FB etc.).
My blog is bilingual (default = CZ, other = EN). in the EN version, the thumbnail shows either FB or other RSS. I am using WPML and it never caused such issues.
Any idea what might cause it? I have tried some plugins to fix the FB thumb but no success. or once it appeared, once not.
I went to debug page of FB and this is what I receive as a result:

“Inferred Property
The ‘og:image’ property should be explicitly provided, even if a value can be inferred from other tags.
Missing Required Property
The og:type property is required, but not present.
Inferred Property
The ‘og:url’ property should be explicitly provided, even if a value can be inferred from other tags.
Share App ID Missing
The ‘fb:app_id’ property should be explicitly provided, Specify the app ID so that stories shared to Facebook will be properly attributed to the app. Alternatively, app_id can be set in url when open the share dialog.”

If anybody could help me with that, I would be soooo happy… please

Thanks in advance,

Michaela