Hi! Thanks for the details.
Looking at your site, the scrolling doesn’t work for me on desktop either. If I resize my window to be smaller, scrolling should kick in and it doesn’t.
I can also see by looking at the markup/css that scrolling isn’t applied to your lightbox like it usually would be. It should say ‘overflow:scroll’ here rather than ‘overflow:hidden’. https://d.pr/i/CvranW
So scrolling simply isn’t being applied. I’d start by double checking that scrolling is enabled specifically for inline content in your FancyBox options for Classic Reloaded.
If it is, and it’s just not applying, I’m not sure why that would be the case without being able to troubleshoot.
One quick fix you could try is to apply this bit of custom css. It will impose scrolling on the lightbox when needed:
#fancybox-content > div?{
overflow: scroll !important;
}