Notification showing even though there is none visible/nothing new
This may occur due to delays with Facebook's own servers, as we do not have any control over notifications that your account receives. We only notify of a new notifications when the Facebook feed informs us. If Facebook is informing us, our app notifies you. If there is an incorrect notification being displayed in your opinion, then it is either that the Facebook's servers are yet to be synced or are temporarily bugged. This should resolve itself automatically when all is in sync.