Mync has setting to define maximum number of storyboard displayed in the side bar. Number of created storyboard might be larger than the number defined by the settings. Set more larger numger in the setting.

1. Choose [Settings] > [View]

2. Change the number at "The number of storyboards displayed in the sidebar". 

3. Close the dialog.

To browse hidden storyboard, click the magnifier in Storyboard tree or choose [Edit] > [Search storyboard].