The exact moment the game successfully authenticates is during initial loading screens. If the game starts and you see the option to "Skip" a cutscene , press it immediately. Bypassing the opening cinematic forces the game to cache session data, stabilizing the connection for the rest of your play session.
The "Failed to restore network connection" error in Tom Clancy's H.A.W.X. 2 Hawx 2 failed to restore network connection fix