Preloader not working

Hi, I'm new to Adobe Animate so this is probably a very basic question but I've created an interactive diagram and on desktop it loads instantly but on mobile devices it doesn't start working properly until everything is loaded. I've selected "Include preloader" and used the Default, which I can see in the images folder but the preloader doesn't appear while the files are downloading. Is there something else I need to do to get the preloader to work?

Any help would be greatly appreciated!

Patti