I had the same problem of Nitish. I say “had” beacause I believe I solved it. But not at all.
I try to explain. Sorry for my english…
I tried to empty cache, to compare source page of my site with original Newspaper, uninstall all plugins, reinstall them, change theme setting, change theme and reintall it. Nothing to do! Sharing on G+ a disaster…
Thumbnails were little and wrong, right the title, without meta description.
I followed the conversation between Nitish and Chris, here, and between Nitish and administrator TagDiv on Themeforest comments. Same frustration for me.
Today I noticed that the number of Thumbnails sharing on G+ was 30 and they were taken from the categories of “mega menu”, not random, but in order of menu. So, if I had in my menu for ex. “art”, “fashion”, “funny”, “sport” and my menu is “Mega menu”, G+ thumbnail was taken from the thumbnail of mega menu preview, in order: art, fashion, etc). If I moved category in menu switching place, thumbnail changes. Interesting, I said!
Going on with my experiment, I noticed that removing mega menu with sub category, thumbnails were correct! I supposed the gap was here. Now I removed [category with subcategory] from mega menu. All is ok. Sharing on G+ is perfect: correct title, correct thumbnail and correct meta description!
But I’d like to solve the entire issue ’cause megamenu with sub category is the peculiarity of this theme.