Our site uses an SSL. The plugin seems to pull resources using http. I've looked around and found that wp_iv_property_URLPATH is defined by WP_PLUGIN_URL which doesn't take an SSL into account. I've patched that up with plugins_url() but we need a more solid fix in case the plugin is updated in the future, which it will be. Thanks.

Correction: The culprit file is plugin.php (plugins/real_estate_pro/plugin.php) around line 238.