1. - It could be the colder weather, especially the recent cold snap. I'm in upstate NY, my winter range is 25 to 45% reduced. Additionally, when below 30-degress, the car's thermal management uses energy to warm up the propulsion battery. This can use quite a bit of juice. It was -5 degrees, two nights ago, my Bolt used 10kwh of electricity that night (while plugged in) to warm up the propulsion battery.
2. - Driving Style. If your son is a more aggressive driver, accelerating hard, driving faster, using the brakes or simply just doing a much greater proportion of highway driving than you normally do, this will still affect the guess-o-meter range for a bit, even after the car was returned to you.
3. - Possibly, the charge settings were changed to a different setting? In my 2018 Bolt, I only have one charge reduction setting, called "Hilltop Reserve", which limits the charge to about 87% maximum. Unless I am planning a long trip, I only charge to this 87% level. I understand that 2020 Bolt's have more variable settings. Perhaps your son adjusted the maximum charge settings?
My present, late December, cold-weather maximum range displays at about 186 miles, using the 87% maximum charge setting). In mid Fall (October), when needing minimal heat or A/C, my maximum range regularly displayed at around 280 miles, again, while charging to 87%.
