Settings::sync() doesn't always work on macOS

We are using QSettings in our tests to setup Qbs parameters.
The pattern we use is the following:
1. Create QSettings object
2. Write some data into it
3. Call sync()
4. Run Qbs (which should read those settings)
5. Remove previously written settings (via dtor of the helper object)
6. Destroy QSetting object

Here are some examples of this pattern: one, two, three

However, it appears that external process (qbs) launched after call to sync() does not get the settings written into the config: one, two, three. It almost looks like a data race like sync() was not called at all.

This only happens on macOS hosts on Github. It also appears that QSettings does not report any error - I've added a check and the tests fails, while sync() appears to be successful. I cannot reproduce that locally.

I am not sure if this is a QSettings bug or an issue with GitHub VMs. However, it happens too often to simply ignore the issue (though it works as expected on Linux and Windows and most of the time on macOS) and I am a bit out of ideas how to proceed further.