When using a mixed protocol site (both http and https are supported) and the WordPress site URL is set to use http, the images from Social Media Widget are being loaded over http, even when the user is visiting the https version of the website.
This is being caused by using WP_CONTENT_URL
in social-widget.php
for composing the plugin URL, a better way to get the plugin URL would be
define('SMW_PLUGINPATH', plugins_url( '/', __FILE__ ));
https://wordpress.org/plugins/social-media-widget/