One strange issue that does not appear always is the following:

When either pasting the exact URL of a K2 item page on Facebook or just pressing the Facebook 'share' link directly on a post of a K2 item, the main information stored in K2 is not retrieved.

More specificallym the Facebook posts do not retrieve the K2 title, the intro text, not even the Item image.

You may see this strange behaviour in one of our sites, opinion24.gr.

Try to paste the following url in your Facebook account and you will get the idea.
opinion24.gr/magazine24/item/3214-12-1-%CF%80%CE%B1%CE%BD%CE%AD%CE%BC%CE%BF%CF%81%CF%86%CE%B1-%CE%B5%CF%85%CF%81%CF%89%CF%80%CE%B1%CF%8A%CE%BA%CE%AC-%CF%87%CF%89%CF%81%CE%B9%CE%AC-%CF%84o-%CF%87%CE%B5%CE%B9%CE%BC%CF%8E%CE%BD%CE%B1-%CE%B5%CE%BA%CF%80%CE%BB%CE%B7%CE%BA%CF%84%CE%B9%CE%BA%CE%AD%CF%82-%CF%86%CF%89%CF%84%CE%BF%CE%B3%CF%81%CE%B1%CF%86%CE%AF%CE%B5%CF%82

Or even try to press share on the respective site's page in Facebook:
www.facebook.com/opinion24

Please advise!

anybody?

Have you modified the Facebook buttons?

No. But the issue is much simpler: Try to paste in the Update Status (in order to share a K2 item) of your own Facebook account the url

opinion24.gr/magazine24/item/3214-12-1-%CF%80%CE%B1%CE%BD%CE%AD%CE%BC%CE%BF%CF%81%CF%86%CE%B1-%CE%B5%CF%85%CF%81%CF%89%CF%80%CE%B1%CF%8A%CE%BA%CE%AC-%CF%87%CF%89%CF%81%CE%B9%CE%AC-%CF%84o-%CF%87%CE%B5%CE%B9%CE%BC%CF%8E%CE%BD%CE%B1-%CE%B5%CE%BA%CF%80%CE%BB%CE%B7%CE%BA%CF%84%CE%B9%CE%BA%CE%AD%CF%82-%CF%86%CF%89%CF%84%CE%BF%CE%B3%CF%81%CE%B1%CF%86%CE%AF%CE%B5%CF%82

and you will get the idea

You said that you don't get this every time. Did you notice anything special about the URL's of the ones that do not work?
For example if you paste www.opinion24.gr/magazine24/item/3214 only you will get the article's information.

I cannot really tell which URLS can or cannot be shared...

I initially thought that it was when K2 items included images inserted in the item's body apart from the Item Image. But no.

Then I thought it was when those images did not have an ALT TEXT description. But not again.

Until today I cannot explain this. And this is quite confusing, especially for our facebook page's likers who cannot share properly the facebook posts!...

It is for certain a K2 issue, but I cannot justify it.

There seems to be an issue with the "D%CE%BC%CE%BF%CF%81%CF%86%CE%B1" characters. To make sure for that try to change the alias for an item with greeklish characters and check on facebook with that new link.

This shouldn't be the exact issue, since all K2 items have greek characters in their aliases whose URLs are 'translated' in that type of characters

Many of these K2 items can be shared, while others not.

I published a K2 item with only latin characters in the alias, opinion24.gr/%CE%BF%CE%B9%CE%BA%CE%BF%CE%BD%CE%BF%CE%BC%CE%AF%CE%B1/item/3268-fitch-european-slow-growth, which can be shared properly.

However, it also has greek characters in the desctiption of the k2 category! (as you can see), that do not seem to bother...

Maybe there are some special character that when transformed facebook cannot process them correctly. For example, in the previous link, opinion24.gr/magazine24/item/3214-12-1-%CF%80%CE%B1%CE%BD%CE%AD%CE%BC%CE%BF%CF%81%CF%86%CE%B1-%CE%B5%CF%85%CF%81%CF%89%CF%80%CE%B1%CF%8A%CE%BA%CE%AC-%CF%87%CF%89%CF%81%CE%B9%CE%AC-%CF%84o-%CF%87%CE%B5%CE%B9%CE%BC%CF%8E%CE%BD%CE%B1-%CE%B5%CE%BA%CF%80%CE%BB%CE%B7%CE%BA%CF%84%CE%B9%CE%BA%CE%AD%CF%82-%CF%86%CF%89%CF%84%CE%BF%CE%B3%CF%81%CE%B1%CF%86%CE%AF%CE%B5%CF%82, the url contained words like "ευρωπαϊκά".

Nope, this is not either.

What we tried is to shorten the url, even including greek characters.

See for example

www.opinion24.gr/magazine24/item/3214-12-1-%CF%80%CE%B1%CE%BD%CE%AD%CE%BC%CE%BF%CF%81%CF%86%CE%B1

So, Facebook cannot probably handle very large URLs.

To make this a permanent solution, we had to change the setting "Include Title Alias" in K2 SEF Parameters.

This should solve the problem, but now our URLs are not SEF...

We suggest that you should really try to provide a solid solution to this problem in a future release of K2 framweork, maybe by narrowing always the Title Alias to a specific (short) number of characters, as an option.