For more information:
My Flint2 (MT6000) is firmwarev4.5.8
I also tried relinking a Creta ( AR750, firmware v4.3.11) and that also failed to connect as the Flint.
I have a Shadow (AR300M, firmware v4.3.7) at a different location, and that one has been running with no issue. I can even access "Web Admin Panel" remotely
Gave up an used the Japan server. Connected immediately.