Strange HTML5 errors on a Wordpress website

Hi,
I notice some odd validating errors on my website. Only until some days ago, site was all validated (except for a single warning on a core file of the Wordpress calendar).
Now I find it full of "errors", without having changed anything, but the last updates of WordPress.
I checked with no plugins and the default theme, but errors are still there.
They seems to be on Wordpress code, are they?
That’s very strange, I would like to understand and, if possible, fix them.
Some examples:

Validating http://www.bluesreviews.it/category/bluesandpics (33 errors)
Error [html5]: ""
W3C error message: "An img element must have an alt attribute, except under certain conditions"

- Seems like all thumbnails on that page are missing of the "alt" tag attribute.
That’s singular, ‘cause I haven’t changed nothing, and they already have alt attribute, so no errors before now. 
Every image on my website have alt attributes.


Validating http://www.bluesreviews.it/ (21 Errors)

W3C error message: "Bad value archives for attribute rel on element link: Keyword archives is not registered”

- That’s on every entry of my monthly archives (again, maybe the WP widget calendar, but when I removed it errors was still there)

W3C error message: "Bad value EditURI for attribute rel on element link: Keyword edituri is not registered”

- It’s the same for “wlwmanifest”, “index” and “canonical” keywords, but they have always been there.

W3C error message: "Bad value google-site-verification for attribute name on element meta: Keyword google-site-verification is not registered”

- My line is: < meta name="google-site-verification" content="GlHj9P4vhSWSq0Odu5QRc8irQHLpHEZSlJ8cNI1y8dg" >, and has always worked well.

Well, I don’t put all the pages here, these are quite enough.
Please, can you tell me what’s happening?

Thank you very much.