A part was failing due to overvoltage/overwork, leading to 3000 or so related warranty events being triggered in the field, so they have to do a fix to affected vehicles. Because it's a regulated field, though I'm sure soon enough they'll be able to just sweep it under the rug.

Every Tesla story on here sees the same "just a software update" thing, but this is a software update to fix a serious issue that hit thousands of vehicles.