I don't know what region you're trying to get news about but if it isn't available online, I'm assuming that when you say web version you mean the Google news page online, there could be reasons for that, the first thing that pops to mind is censorship, but I would imagine people are finding a way. You might try searching something like, how to access xyz region google news, and see if anyone has posted a work around or a solution to access.
As for why it might work on the app vs the browser version, if the region is being censored or blocked from access in some areas the app may by-pass that filter. Otherwise I haven't a clue. Try the search thing, let us know what region you're trying to access vs where you are and tell us if it worked.
Best wishes.