I suspect you really don't have a problem at all. With the information you have given, everything is probably fine. The range displayed after a full charge is dependent on recent driving and is highly variable. And in practice, no two trips are ever really the same. Here's a possible explanation, but just one possible conjecture. You had a sizable trip at 5.6mi/kWh, but a few weeks ago. So, maybe some short trips in between had lower efficiencies. Then, two weeks later, the 5.6mi/kWh trip falls off the back end of the algorithm, and boom, the next full charge shows a lower average. You never said that you consistently see 4.1mi/kWh, you only calculated it, right? Do you actually write down the miles per kWh and odometer change every single time you drive the car and calculate a weighted average, for weeks, months? Or, similarly, you can look at the kWh since last charge display and the total odometer change since last charge. But all of this is really only meaningful over many charges before you'd conclude there's a problem.
Stuff like this happens all the time. Say we have a cold spell. It's been 55F for a few days and I had the heat on. Oh no, after a full charge, I only have a 52 mile range. Of course, my range hasn't changed at all. Now, it's 70 degrees and sunny. I drive for 10 miles. My range changes from 52 miles to 48 miles. I drive another 5 miles. My range stays at 48 miles. I drive another 5 miles. My range goes up to 50 miles. Eventually, things average out.
Here's a little trick I use, especially if the projected range after a full charge seems low. After a full charge, at the beginning of your trip, take the displayed range and add it to the miles on the odometer. Just keep track of the lowest two digits. Then keep track of the sum as you drive. By doing so, You're getting actual miles vs projected miles. You'll know far more accurately what your range will end up being. Here's an example:
Guessometer: 69 miles, odometer: 46,375 miles. sum (truncated to two least significant digits): 69+75 = 164 = 64. Keep that number in your head (or write it down). If you drive 10 miles, but the range only drops by 8, you've added 2 miles to your original 69 mile projection. At any time, you can just add the two again, and if it's more or less (than 64 in this case), that's how much your range went up or down by. Of course, like the stock market, past performance is not a guarantee of future results
