Magento – Magento 2 : Mixed Content Error Block HTTP Request an HTTPS page

Final I found the solution.

Replace the Base URL from http://example.com/ to //example.com/

CAUTION! The change is not allowed in magento2 admin.

I made it in MySQL in table cron_config_data and record with path='web/unsecure/base_url'. After cache:clean and varnish restart everything works smoothly in frontend.

Unfortunately problem remains in Backend. Magento2 redirects to this url: https://example.com/admin_mine/index/example.com/admin_mine/index/index/key/...

This last problem solved by simply change the Admin base url from Stores -> Configuration -> Advanced -> Admin -> Custom Admin URL = https://example.com/

Did you install ssl for localhost server?

Try to add it:

sudo nano /etc/apache2/apache2.conf

Modify section:

<Directory /var/www/>
        Options Indexes FollowSymLinks
        AllowOverride None
        Require all granted
</Directory>

to this

<Directory /var/www/html>
        Options Indexes FollowSymLinks
        AllowOverride All
        Require all granted
</Directory>

After that, run command

sudo a2enmod ssl

sudo a2ensite default-ssl

sudo a2enmod rewrite

sudo service apache2 restart