I have used it and the Flightstick at airports without internet previously without issues. The Flightstick can definitely be used without internet connection indeed I have just tried it on my laptop and it is working away fine without internet
Just switched off the internet on my main computer and closed down and restarted RB with my Micro RB and have 3 aircraft showing in MyFlights so it does work without internet as I suggested
What log in details are you using, the ones for your original box or your Radarbox log in details. If you are using your Radarbox24 log in, try it with your original Radarbox log in and see if that makes a difference
Just had it confirmed by support that using your PGANRB log in you will have no problems but if using your Radarbox log in you require internet
Alan