Possibly related. I'm having trouble with 93 octane in NY. My car's knock sensors retard timing and utterly kill MPG if the fuel is not a true 93. I had one batch so bad, I got 16 miles from full to 3/4 and not quite 50 miles from full to 1/2 tank. It was so poor, and the car so slow, I couldn't finish a 60 mile trip to the airport on the last half a tank.
A little research led me to the FACT that organized crime is adultering the fuel, possibly diluting premium with regular and charging the station for premium. That explains why it happens at random local stations, and not anywhere else.
So when I see a massive MPG drop, I go to a station out of state. And walla! MPG is back up to 28.