error 404 only on home page after upgrading to wordpress 4.5.3

Hi everybody.

After upgrading to wordpress 4.5.3 i get error 404 on my homepage https://www.ninamasina.it

Everything seems fine as i’m logged as administrator, but everyone else get error 404 when trying to reach the homepage – even me, as i log out as admin.

Other pages – for example, the about page – display correctly, even every entry of the site.

I tried to re-set permalinks, disable all the plug-ins and change to default theme without success.

On the host side, I re-set all file permissions to default (755); .htaccess file seems ok:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress

I create a free account on Onpage.org site and i let it crawl my homepage: it gets a 404 error, giving me this result:

Status Code 404 – Not Found
The requested resource could not be found but may be available again in the future. Subsequent requests by the client are permissible.
date Tue, 02 Aug 2016 18:39:05 GMT
server Apache
x-powered-by PHP/5.6.19
expires Wed, 11 Jan 1984 05:00:00 GMT
cache-control no-cache, must-revalidate, max-age=0
pragma no-cache
link <https://www.ninamasina.it/wp-json/&gt;; rel=”https://api.w.org/&#8221;
keep-alive timeout=5, max=100
connection Keep-Alive
transfer-encoding chunked
content-type text/html; charset=UTF-8

i can’t figure out what is not working…

Any ideas?

Thanks in advance,
mm1