@Michel Bujardet Is there some versions of the system which prevent writing there ? Or which wipe the data somehow ?
Every once in a while I get these kind of reports also. I've never been able to narrow it down, except that my first report came from High Sierra, so I suspect it be something with APFS.
@James Sentman I recently moved all the data to a folder in Documents instead as there are folders in there that users need to be able to access and getting to Application Data in the Finder requires extra steps since by default you can’t get inside your Library folder via the Finder.
I had an argument with the App Store reviewers over this. Recently they enforced the policy that "user data" must be stored in the Documents folder, even for shoeBox style applications. Which I agree with but...
There is no provision for a Sandboxed application to have access to a subfolder of the users documents folder. So this must be done with a Security-Scoped Bodgemark and asking the user on first launch where to write their data too. The main problem with bodgemarks, is that they're fragile and when they break you can't get any meta data about the file they used to link to. So when it goes wrong, you can't even suggest to the user where to look or the name of the file that they'd chosen. You know for security reasons <facePalm/>. The second major issue with using a SSB, is that the application must request and release access (within 90 seconds), every time it wants anything from that folder (including meta data). It made database work impossible (although a workaround is to create the database in the application support folder, leave it there, but hardlink the file into the users selected folder, just make sure that your application always uses the file in the app support folder, not the user location).
So I filed a feature request; which was shot down within days. I tried to argue my points; but it feel on deaf ears.
@Emile S What about a MenuItem that display that user dealing folder data ?
I had this already in my application and informed the App Store reviewers about it; they don't care. The policy is...