Are your a Tesla Model S owner that experienced a range decrease greater than the average customer? I have been charging my car between 60% and 80% on a daily basis to preserve my expensive battery pack. This resulted in decreased range estimation.
(One picture is in miles, the other in kilometres, I used to be able to range charge @ 435km and I am now down to 389km)
According to Jerome Guillen (Tesla VP, WW sales and service) and Tesla engineers, it is due to an inaccuracy of the range estimation algorithm:
“Our engineers apologize for the inaccuracy of the existing range estimation algorithm. Right now, they are beta testing improvements intended to resolve these issues, regardless of how your car is charged. If you modify your daily charging behavior to charge at the top end of the “daily” range, you should see your fully charged range increase over time. Note, this is an estimation problem that can take weeks, if not months, to correct, depending on your driving behavior.”
This might also explain my last supercharging session. I waited 2 hours and never got the “Charge completed” message. I kept on getting the “Re-calculating” message.
Following Jerome’s recommendation, I started charging at 90%. To be continued…
On another note, how many car companies apologize? Tesla continues to amaze me. Every company faces challenges. It is how they handle and fix problems that makes this car company very different. This is one of the many reasons for their success.
Ma Model S / My Model S 
Tesla ended up fixing my problem and I got my range back.