offline mode not working

I use this plugin togeter with onesignal.
I have defined an offline page.
I have turned on pre-caching
I have ticked the onesignal box under tools.

But when I load the web app on a iphone or android phone browse all the pages, close the webapp, turn off wifi and mobile data and open the app again I get an error that I do not have internet acces and that the page cannot be opened. “Safari cannot open this page as your iPhone is not connected to the internet”

The page I need help with: [log in to see the link]