My similar vintage similar miles S75 does this a lot now with recent firmware releases. Not sure why, but it’s very consistent. If I park with less than 20% SoC without charging immediately the car “loses” 5% SoC within 20-30 minutes of sitting. The BMS seems to get confused or is protecting some extra charge buffer or something. The car eventually gets the 5% back, usually shortly after charging (which results in it overshooting my set charging limit by 5%).When I ran it down to 7%, I let the car sit and go to sleep for 1 hour, when I returned, the car was showing 1%, very odd.
Strange, but seemingly harmless. I’m confident Tesla isn’t gonna do anything for you until the battery actually fails with errors on the dash - so I’d not waste much time trying to convince them.