Android Offline Folders - cache and Dropbox out of sync

[Peter S.32]

I have opened a File (pdf) which is in an offline available Folder from inside the Dropbox app in a third-party app (Xodo). I left it open for about a week in the background. After closing it, it did not sync back to dropbox: the internal viewer and the Web Browser show the unchanged File. However, when I reopen the file from the Dropbox app, I see the changed version. In the local cache /sdcard/Android/data/com.dropbox.android/... there is the changed version pending, but no upload seems to happen.
What to do to force syncing with the cloud?

[Sanchez]

Hey Peter,

Does this occur when you use Wifi only, or mobile data only?

Do other files and file types have a syncing issue, or does this happen just with PDFs that you edit with Xodo? This may be an issue with Xodo, as Adobe is the currently supported PDF editor that will send the updated file back to your Dropbox. 

You may also try to keep the third party app in the foreground, as auto-updating while the app is in the background isn’t currently supported. The only exception is when Android devices are connected to power, offline files sync in the background (https/www.dropbox.com/help/9279).

Please also check that you have the latest version of our app, and that your Android operating system is updated. What version of Android are you on? 

Alternatively, you can submit a support request here https/t.co/JzCu5Ol0GV so an agent can troubleshoot more closely with you.

Let me know when you can.

Thanks

[Peter S.32]

My Phone is a Samsung Galaxy Note 4, Android 6.0.1

So far, I encountered those problems only with Xodo.

Keeping the App in the foreground is unrealistic on a Smart-Phone: I correct student homework with the pen in the train - when the train arrives, I'm interreupted till the next day.

I understand the help differently, the Dropbox app has to be in the foreground for sync? Generally, I tried to find some technical background how the offline folders work. How are the files handed over to the 3rd party apps? Do the access the copy in the cache in the local file system? Do they send the changed file thtough some API? A general Android API, or a special Dropbox API? I could not find such information.

One strange thing is when I upload a number of PDFs (from a Camera Scanner) to Dropbox to a folder made available offline, the PDFs are downloaded again when I open them from the Dropbox App. Does upload to the Dropbox bypass the Dropbox app? One would expect that Upload to Dropbox means that the files are first copied to the local Dropbox App cache, which then syncs them up when there is a connection. Thus, there should be no need to Download the same files again. I'm very interested in such details, as I need trust in a technology to use it.

[sjo]

I have this problem too when using Xodo. Have you ever found a way to force a sync back to Dropbox? Some files sync back fine, but others seem to be "stuck" in a local cache. Even when I close those files within Xodo and open them up again in Xodo (through the Dropbox interface), the local file opens again, but it never syncs back to my Dropbox folder.