In article 2015091320455242577-savageduck1@REMOVESPAMmecom,
Savageduck wrote:

dropbox on ios syncs when the app is run. if there's no connectivity,
you can only see what has previously been synced.

I have a pretty active Dropbox account and many of my image files have
been loaded in DB for some time and have always been accessible on my
iPhone and iPad with the DB app. However, if I am offline the iPad
cannot connect with the DB server and cannot access the image files on
that server. The result is, offline I see no image files stored on DB
even those which had previously been available when online.

you need to mark files as favourites for them to stay local.
it didn't used to work that way.