Stuck O2 Sensor? How?

[Bmwtvboy]

SES light came on, went off over a few days. I know that's more or less EVAP issues so I don't panic. Scanned and got some interesting codes:
P0140: O2 sensor circuit No activity, Bank 1,Sens 2 . Days later this code,
P2270: O2 sensor Signal Stuck, lean bank 1 , Sen 2. Cleared, days later again.
I took pics of additional readings while running, but nothing else stated issues with O2 that I could understand.
Is Bank 1 the front 3 cylinders from radiator back? Is Sen 2 post cat?
Gas mileage is what it's been for months. Now using reg 87 oct gas.
It's a 250K miles 01-3.0 auto setup.
I'm guessing it's not that serious.
Thanks