The connection to “domain” is not secure

I use this for my htaccess force-SSL rule on my multisites (actually, on all sites).

RewriteEngine On    
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

Not sure, but bet that off is better than !=on .A resource you can use to test htaccess rules is https://htaccess.madewithlove.com/ .