TwinCAT stops sending notifications after a few seconds

Question

using the ADS.NET Interface for TwinCAT (Package Beckhoff.TwinCAT.Ads 6.0.235) together with TwinCAT 3.1.4024.42 (as of today) we are experiencing an undesired effect.

When connecting to a variable by notification with a cycle of notification update of 1 ms, after a few seconds no more notifications are being sent, when the connected variable frequently updates.

Here is a sample how the notification is being setup:

 public bool ConnectVar(object userData)
    {
        bool ret = false;

        ConnectTc();                // Connect to TwinCAT, create _tcClient
        _vartype = GetVarType();
        if (!(_vartype is null))
        {
            NotificationSettings settings = new(_transmode, _cycleTimeMs, 0);

            _handle = _tcClient.AddDeviceNotificationEx(Varname, settings, userData, _vartype);
            _tcClient.AdsNotificationEx += _tcClient_AdsNotificationEx;

            _handleRw = _tcClient.CreateVariableHandle(Varname);
            if (_handle != 0 & _handleRw != 0)
            {
                ret = true;
                _connected = true;
            }
        }

        if (_connected)
        {
            _lastReceivedValue = Value;
            _lastReceivedValueTimeStamp = DateTimeOffset.Now;
        }

        return ret;
    }

And this is the notification handler

    private void _tcClient_AdsNotificationEx(object? sender, AdsNotificationExEventArgs e)
    {
        _lastReceivedValue = e.Value;
        _lastReceivedValueTimeStamp = e.TimeStamp;
    }

So when setting the Update Cycle time to 1 ms, after a few seconds (about 5) no notifications at all arriving anymore. No errors / exceptions are being created, the notifications just stop. When deleting the notification and adding it new, values are being received again - for 5 seconds. When increasing the cycle time to 2 ms, it seems to "work". Somehow this effect is hard to handle as one can not be sure, what conditions are necessary ...

So, did anyone experience a similar problem and know how to handle this ?