yuopi

private void comboBox1_SelectedValueChanged(object sender, EventArgs e)
        {
            departComboBox.SelectedItem = _departmentList.FirstOrDefault(d => d.Id == _clientList.Find(item => item == (Client)clientComboBox.SelectedItem).DepartmentId);
                
        }

StreamReader _reader = new StreamReader(path);

public string GetNext()
{
    string line;

    while ((line = _reader.ReadLine()) != null)
    {
        var message = WorkWithLine(line);
        if (message != null)
            return message;
        }
        return null;    
    }

}

public string WorkWithLine(string line)
{
    var ip = Regex.Match(line, "IP: .*?\n");
    if (ip.Value.Length > 0)
        return null;          
    return ip.Value;
}

Использование:
void Do()
{
    string msg;
    while(while ((msg = GetNext()) != null) 
        Console.WriteLine(msg);)
}