Google shows the wrong thumbnail when sharing post

Hi everybody. I’m experiencing a trouble when sharing posts on Google+. Up to about a month ago eveything worked fine and Google+, as Facebook and Linkedin, shared my posts with their respective featured image as thumbnail, according to the settings I choosed by All In On Ceo plugin (which is the one I’m currently using).
Then, suddenly Google+ started publishing random thumbnails, then no thumbnail at all and, in the end, the same thumbnail for any posts (i.e then snap of a brochure of a meeting where I happened to be one of the speacker) regardless of their featured image and regardless of the fact that this fixed image has nothing to do with their respective contents.
The same thing happens if I customize the image using All In One Ceo’s panel located at the bottom of each post.
I have tried to check some post on Google’s Structured Data Testing Tool, but any problem has never been detected: it recognizes the exact thumbnail, but, when sharing, it shows the above mentioned fixed image.
This is the shortlink to one of the test:

https://developers.google.com/structured-data/testing-tool?url=http%253A%252F%252Fwww.jusdicere.it%252FRagionando%252Fla-causa-di-non-punibilita-del-reato-per-particolare-tenuita-si-applica-anche-ai-reati-tributari%252F

It’s worth adding, I did not set the fixed image that now Google plus uses as og image anywhere and that everything is still working fine as to Facebool and Linkedin sharing.
I’m using wordpress 4.1.5 (still not updated to 4.2.2 because I am waitng for all my plugins update to that version), with All in one CEO, as stated above.
No way to handle that situation. Any idea would be greatly appreciated. Thanks