I am using the same plugin and it works quite well for us.
I think it needs to be considered that it is a WordPress plugin. So there simply could be a conflict with other WordPress plugins. In fact, we have faced with similar situation recently. To find the reason of the issue – we tried to deactivate all plugins on our site one by one. It was helpful, we have found the plugin which caused the conflict.
But situations could be different, I just wanted to share my experience of using this plugin.