Ours dropped to mid-40s mpg last week, accompanied by a hot front right hub.
Investigation revealed nothing much, caliper sliders free enough, some dried out brake grease around the pads, which were fairly tight. Cleaned up, greased and refitted pads, and slipped a bit of liquid silicone behind the piston dust cover. Seems okay now, no longer binding. We'll see how it goes... hope the mpg recovers!