If I had to name one plugin that you should be extremely careful when making an upgrade, it is Yoast WordPress SEO. It is really a good habit to go through all the settings and check out source files to spot changes and strange behavior.
In the changelog for 1.5.2.3 update of Yoast SEO we read:
Note: if you already upgraded to v1.5+, you will need to retrieve your Facebook Apps again and please also check your Google+ URL. We had some bugs with both being escaped too aggressively. Sorry about that.
If, besides a personal profile, you have a Google+ business page, you most probably pasted its URL address at SEO/Social/Google+, in the field labeled Google Publisher Page:
Things are fine, if the address includes digits, but if you already acquired a unique page name starting with a plus, you should double-check the address.
The plus in the URL might be missing after the update of Yoast SEO to 1.5.2.3.
Without the plus the URL links to a 404 page on Google. Plus, the blog and the Google+ profile are not connected any longer.
More on WordPress:
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