I'm gad you've been able to find the answer to your problem.
Thank you for letting me know.

Here's some more information for others reading this forum thread and encountering similar issues.

Your screenshot shows the Splash Page.
The Splash Page is a placeholder for the gallery which is displayed by default on small screen devices when the gallery is embedded in a web page alongside other content (rather than displayed on a page of its own with dimensions of 100% x 100%, filling the browser window) and may may too small to be usable.
The Splash Page is essentially an image link for the gallery which displays an image (by default, the first image in the gallery) and some text.
When the user clicks or taps the Splash Page, the gallery is expanded to fill the browser window (giving the images more space to be displayed).
More information about the Splash Page can be found in the Screen Modes section of the Gallery Tour.

If you want AutoPlay to start once the gallery has been expanded from the Splash Page, set autoPlayOnLoad="TRUE" (in JuiceboxBuilder-Pro's 'Customize -> Autoplay' section) in conjunction with showSmallThumbsOnLoad="FALSE" ('Customize -> Thumbnails').

If you would rather not use the Splash Page, then set showSplashPage="NEVER" ('Customize -> Splash Page').

Alternatively, you could force the gallery to be displayed in Large Screen Mode (which, by default, does not use the Splash Page) on all devices and in all browsers by setting screenMode="LARGE" ('Customize -> General').

For reference, all the Splash Page configuration options can be found here.