P0155 is tripped by a circuit fault in the upstream heated O2 sensor (bank 2). No other code throws along with this huh?
Not sure on the drivability items you noted. I would think you would find P1150, P1151, P1152, P1157 or P1158 if it was an A/F issue in addition to the circuit fault. With no other drivability issues or codes, I would guess you may have got some water in the harness connector on that side which tripped the fault OR you may have some premature corrosion of the mating terminals, yada, yada, yada.
Try clearing and see if it comes back. If it doesn't, it was a freak-fault, if it does, it could be a couple other things in addition to the ones I mentioned above.