I can no tell for sure without downloading and installing the plugin and playing with it but I can tell you the most likely reason – and I stress this may not be it.
WordPress allows plugins to work by the use of ‘hooks’ known as action and filters. One of the most common is called ‘the_content’ which allows a plugin to add/remove or change the actual content of a post or page. SP uses this to display your forum.
It is possible that your Social Media plugin is also using ‘the_content’ to add it’s display components.
The problem with using these hooks – if that is what is happening – is that, if not defined in the code when called, the order they are used can be random. So it might be – and again I stress the ‘might’ – that your plugin is simply getting the first bite followed by the forum.
If you know your way around the plugin code you could look for an add_filter(‘the_content’ ‘xx’) in the code and give it a higher priority which, in theory, should force it to be actioned later in the processing.
So – might that be the answer?