I really think Sub and Airship zone discovery is broken. I've been sending out my airships and subs for 2 or 3 months to discover new zones and they still have not.
I have 3 airships all lvl50. I keep sending them to Sector 21 so they can unlock Sector 24.
I have 2 subs lvl79 & lvl65. I keep sending them to Rimilala Trench Bottom so they can unlock Sunken Vault.
Nothing has unlocked for me in months. IDK what's wrong. Is it broken, or am I doing something wrong?