my estimated range is stuck at 51 miles

hey people! I just climbed from 1000 ft elevation to 6500 ft elevation. San Bernardino ca to big bear, ca. its about 40 miles of switchbacks, steep grade. I've done it a few time before with no issue. the percentage of battery level always drops rapidly as I climb the mountain as does the estimated miles of range. I usually arrive with around 20% left (starting with 100% down the mountain). same was true tonight except that at 40% battery level it said my range was 51 miles. and it was stuck in 51 miles for a good part of the 45 minute journey. then I turned the climate control off and all of a sudden it said range was 16 miles which would be completely accurate based on my other trips up here. any ideas what could have caused this?