Excuse me, 2 tings:
1 – The problem is only in the child theme; if I switch to Hueman all is ok.
2 – I forgot System Informations:
# SITE_URL: https://silvioto.altervista.org
# HOME_URL: https://silvioto.altervista.org
# IS MULTISITE : No
# THEME | VERSION : Hueman | v3.1.6# WP VERSION : 4.5.2
# PERMALINK STRUCTURE : /%postname%/
# ACTIVE PLUGINS :
ABASE for Accessing MySQL Databases: 2.6
Antispam Bee: 2.6.8
BackWPup: 3.3.1
Contact Form 7: 4.4.2
Display Posts Shortcode: 2.6.2
Duplicate Post: 2.6
Email Subscribers: 3.1.4
Favicon by RealFaviconGenerator: 1.3.4
Hueman Addons: 1.0.4
iframe: 4.3
Inline Spoilers: 1.2.5
Italy Cookie Choices (for EU Cookie Law): 2.4.4
JP Widget Visibility: 3.9.6
Light – Responsive LightBox: 1.1
Maintenance Mode: 1.4.3
Regenerate Thumbnails: 2.2.6
WP-PageNavi: 2.90
Yoast SEO: 3.2.5
PHP Version: 5.6.18
MySQL Version: 5.1.71-community-log
Web Server Info: Apache
WordPress Memory Limit: 40MB
PHP Safe Mode: No
PHP Memory Limit: 128M
PHP Upload Max Size: 20M
PHP Post Max Size: 20M
PHP Upload Max Filesize: 20M
PHP Time Limit: 30
PHP Max Input Vars: 5000
PHP Arg Separator: &
PHP Allow URL File Open: Yes
WP_DEBUG: Disabled
Show On Front: posts
Page On Front: (#0)
Page For Posts: (#0)