I have been advised that this is a support issue rather than a bug.
I use a number of PDFs stored as stealth and displayed in pages using iFrames. They display fine on desktop machines but not on mobile devices. I understand this may be a browser issue rather than a moodle issue. The usual workaround is to use the google docs embedded file viewer but I am unable to get that to work on my moodlecloud site. It seems to display the html code for the login page rather than the specified pdf. Thanks