The sticking brakes is definitely the first thing to look for.
Also the 'guessometer' makes it's estimate based on past driving plus the current state of the car.
The estimates can vary wildly depending on these things.
For example, I took my brother out for lunch to a restaurant on top of a hill.
The next day (after I'd cruised home downhill all the way) the guessometer said that I had 84km of available battery range...
Load, heating/cooling, driving style all play a part.
But for now, check the brakes first, that's the issue that has caused the biggest range changes so far.
2014 PHEV Aspire, Arctic Silver;
Hayman Reese removable tow bar;
1.5kW Solar, grid connected.