Open Graph does not work properly

I recently noticed that the og:title tag is not displaying correctly and I don’t know how to fix it.

In the “Title and meta” settings I have set these tags for pages and for posts: %title% %sep% %sitename%

In the source code the schema appears correctly, showing the og:title with the page/post title followed by the web title, but if that same link is shared via Facebook or WhatsApp only the page/post title appears (%title%).

I have gone to the Facebook debug page to see what it is extracting and curiously it only extracts the page/post title.

If you want you can check it yourself with any link on the web, for example this one: https://iesdimreus.cat/estudis/eso/

For what it’s worth, I have the plugin configured to only index certain pages. I have checked if the problem persists with indexed pages and it still shows only the title.