NEVPNStatusDidChangeNotification - invalid

-I've implemented a VPN app (with Packet Tunnel Provider).

I have an ovserver for NEVPNStatusDidChangeNotification.

When the user press the "connect" button, 90 % of the time I get the notifications where the connection.status goes from Disconnected to Connecting and then to Connected.

But I've already encounterd several cases, where the connection succeeded, but the notifications I got were

Disconnected -> Connecting - > Invalid

And as I said, the connection been made and the VPN had been activated, so why I got the Invalid state ?

Edit:

Those are some of the system logs:

name = <40-char-str>
    identifier = some-identifier-I-dont-know-1
    applicationName = myApp
    application = myAppBundle
    grade = 1
    VPN = {
        enabled = YES
        onDemandEnabled = YES
        onDemandRules = (
            {
                action = connect
                interfaceTypeMatch = any
            },
        )
        protocol = {
            type = plugin
            identifier = some-identifier-I-dont-know-2
            serverAddress = <16-char-str>
            username = <24-char-str>
            password = {
                identifier = some-identifier-I-dont-know-1
                domain = user
            }
            passwordReference = <67656e70 00000000 00000417>
            identityDataImported = NO
            disconnectOnSleep = YES
            disconnectOnIdle = NO
            disconnectO

Updated network agent (inactive)

vpnStatusDidChange: Invalid

NESMVPNSession in state NESMVPNSessionStateIdle: update configuration
NESMVPNSession: Received a start command from myApp