Hi there,
Thanks for reaching out!
OpenSongApp (Android) and JustChords (iOS) deal with songs and sets slightly differently, but do their best to synchronise what they can via the OpenChords server - we both promote each other's apps for this very reason!
If you are willing (check it is ok with your friend as well), send me the link as a private email to the shared folder and I will test that for you. If your friend is using songs that aren't native JustChords files (e.g. images/PDFs, this could be the issue with the 'missing' songs, but I'd need to check that out.
To access any synchronised sets on your device, you have to make sure you select the OpenChords set category to be able to see the set. To load theses, go to Settings > Manage Sets > Load sets. From the page that loads, click on the category list and select OpenChords. You should then be able to see and load synchronised sets. In OpenSongApp, the setlist simply has links to the songs on your device (so they have to be synchronised as well).
This will take you through the steps.
Please let me know how you get on, and if you need further help (or message me privately with the openchords folder link)
Gareth