apt (and all programs on top of apt like HAM and fapman) works like this: referenced by a sources.list it grabs some informational catalogues form specified repositories and builds some kind of lokal database out of them. This lokal database you can use as long as you want to but it is only as actual as your last update. Therefore it is usable for offline searching in the database but you will not see newer updates until you re-download the catalogues again (e.g. run the update).
Upgrading instead means bringing an installed application to a newer version. This requires in first place to have an updated database of available applications (e.g. having run the update). Of course, for updating as well as upgrading you need a connection to the internet.

why not include an equivalent of apt-get update && apt-get upgrade in the app?

After erasing the cache directory you updated the catalogues and after reinstalling you verified there are repos activated?

Did you have a look at fapamns log (in the menu)?

Is it possible that dates aren't fetched and the program stalls for this reason?

What do you mean? You already have update and upgrade available.

And did you see the log for details? Would you mind sharing these details with us so we could probably help you?

here is what the log says