Sudden MPG drop in the morning

You have not driven the car for enough miles to achieve a higher MPG. Ig you only drove 7 miles and averaged 54mpg then allowed the car to idle and then backed it out of the driveway you were getting 0mpg. That is enough to drop your MPG pretty drastically. Just keep driving the car. By then end of your tank you'll be back where you expect it to be.

 

Were you running your heat?

Heat=ICE running, correct?

 

If the car was left on (READY mode), the ICE will start and stop to keep the traction battery charged. Did you or your husband notice a strong exhaust odor inside the garage in the morning? If so, he left the car on and your gas mileage would drop significantly overnight.

And, as F8L said, you haven't put enough miles on the car since the fill up to give you an accurate MPG reading anyway.

 

Between the gas station and home, you burned (7 mi) / (54 mpg) = 0.13 gallons.

When you checked the gauge this morning, after hubby moved it, it had burned (7 mi) / (41 mpg) = 0.175 gal, meaning an extra 0.045 gal was burned somehow.

Did hubby let the car warm up? That sounds about like my normal extra fuel consumption during the warmup process (while moving), and much less than the 0.06 gal it burned sitting in its parking space recently while I was scrapping ice of the windows -- and that got it only to 125F, not a full warmup.

The more miles you roll up since last resetting the gauge, the smaller the numeric MPG hit with each warmup. But the amount of extra fuel burned each time should be about the same.