It seems the order of QML Imports does matter in specific cases:

import QtQuick.Controls 1.0
import Qt.labs.settings 1.0
import QtQuick.Controls.Private 1.0

ApplicationWindow {
    width: 1300
    height: 900
    visible: true

    Settings {
        id : appSettings
    }
}

Leads to a runtime error

qrc:/main.qml:10 Element is not creatable.

Moving "import Qt.labs.settings 1.0" after "import QtQuick.Controls.Private 1.0" fixes this.

As both imports provide a "Settings" type (one as QML singleton), the engine should produce an error message that there exists an ambiguity.