Offline files not downloaded when accessed programmatically (macOS)

Not sure where best to address this question, but it would appear to be API-related...

We've got an existing app which has been working OK until recently on both Windows and Mac platforms, which accesses XML files stored in the user's local Dropbox folder.  (The app is mainly cross-platform C++ with a thin layer of platform-specific code, which on the Mac side is Swift-based.)  Until now, this has worked fine; while we use SwiftyDropbox on the Mac side for other communication with Dropbox, we haven't had to download the files through the API, we've relied on the Dropbox client app for that.

But now a user, having done a clean install on a Mac, is reporting that the files are showing up as zero bytes; this would appear to be because they're arriving from the shared Dropbox folder and have not been synced locally for offline access, which I understand is the new default behaviour (though I note that the user is not yet running the FileProvider version of Mac Dropbox).

The concern is that, while clicking on the file in Finder in the local Dropbox folder to open it triggers a sync and successfully opens the file...  opening the file from within our C++ code doesn't.  When we try to read it using standard ifstream and ostringstream calls, we get an empty buffer.

Once we double-click the file in Finder, it reads it correctly (without even restarting our app).  And the open calls still work fine with the same version of the Dropbox client on other machines, with files which are synced locally.

So question #1 is, what do we need to do to open the file inside our program the same way as double-clicking in Finder?  That would seem to be the simplest way to make the problem go away.  (We could do this in either the C++ or Swift code as needed.)

Question #2 is, is there any way to force these XML files *programmatically* to be available offline?  Again, that would pre-empt the whole problem.  Is there anything in the SwiftyDropboxAPI which can set a file to be synced locally?

Failing that, our least-preferred solution is to download the XML file as a file through SwiftyDropbox, bypassing the local sync directory, and reading it like that.  This would require a wider-scale re-engineering of our app, so we'd rather not do that at this point if we can help us.

Which raises question #3 -- is this an issue which can be fixed by having the user upgrade to the FileProvider version?  Will that resolve those kinds of sync issues?  They're currently using client version 206.4.6506 on Sonoma 14.6.1; are there known issues there?

(For the record, there seems to be something flaky about their Dropbox installation to begin with; the Dropbox shortcut link in the left-hand pane of the Finder window isn't showing the Dropbox icon, and there are no sync icons.  I've suggested a reinstall, and will update as we get more information.