I had to completely re-flash the device. The menus that you are referring to (disabling flight mode) did not appear anymore, they are blocked by the unlock app.
I installed the pin after that, which saved me already a couple of times. The last time was with this weeks app "update", after which my ring was not recognized anymore.

I put my device (Sony Experia Z2 tablet) in "Flight mode" in a plane, powered it off and didn't realise NFC-read-out would be disabled too.
I used a Google app-specific generated password, which I forgot to write down, because I don't like (as so many other people) to use my Google master password for a 3-party app.
But I'm not so sure either if the Google authentication would be working at all in flight mode.

So now I'm completely locked out, because I can't use the ring, the Google authentication and I can't switch off the "Flight mode".
I even can't factory reset my tablet because I can't unlock it.

Any suggestions?