Dev-Question; /data/data not persistent

I'm using an unrooted Razr-I XT890 with Android 4.1.2

When using the app "Syncthing-android" I run into what seems to be a Razr-I specific problem described below.
Syncthing is a multi-platform secure syncing app and Syncthing-android is a port to the Android platform.

The particular problem is that the the config data (node identity, keys etc) get lost after a reboot of the phone.
When used the memory status of the app shows 72 KB of "data", and 0 KB after a reboot.

One line in the logcat caught my attention:

However, if the app is exited or "killed" and restarted, the data is still available and the app uses them.
But it is gone after a reboot. According the original developer this happens only on my system.

I'm hoping that somebody recognizes this pattern and can give me/us a hint to its origin.

I'm not the developer of that particular app, rather an interested user, who happens to be a developer, but not very proficcent when it comes to Android apps. However terms like "logcat", "intent" or "service" don't scare me

Sorry if this sub-forum is not the correct one for posting this kind of question. The one which seems more appropriate is not accessible to me.
This relates to issue 24 of syncthing-android on github - sorry, I can't post external links here yet.

Thank you for your suggestion.

We found the bug (see original thread on GitHub).

For future reference:
The "official" folder to store persistent data can be obtained by the API call getFilesDir().
The deleoper used getApplicationInto().dataDir

The first one points to /data/data/appname/files/
The second one points to /data/data/appname/

It seems that the Razr (contrary to other phones) deletes files in /data/data/appname/ which are not stored in a subfolder.