Hi,
Check out this ticket dating back some years, and the solutions related to max_input_vars and see if it helps. https://core.trac.wordpress.org/ticket/14134
Same issue here. Menu won’t save in 4.3 Any solutions?
I have same issues and solved it!!
here my htaccess:
# 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]
php_value max_input_vars 5000
</IfModule>
# END WordPress
So you need to add this line: php_value max_input_vars 5000
still if you have same error then if you are using Yoast SEO Plugin just deactivate and try..
Thanks