@Penn - You have not stated what the conditions were around your observation of having lost 26 miles parked. You did include in your original post a link to an image of warning that pops up if you park the car when the battery is at around 20% SOC or lower.
Is this the situation for your observation? You've driven the car, probably extended distance such that the battery was warm, but then parked it at a 20% SOC or lower but not plugged in? If that's the case, then your observation is due to the available energy from the battery naturally reduces as the battery temperature cools down. This is not abnormal or an indication of battery failure, but just the nature of how the BMS judges the available, usable energy. This drop is much more significant at low SOC, which is why Tesla actually now pops up the display message telling you that you should plug the car in as range may drop.
If that's not the situation, then you've not really provided sufficient information for any of us to give you a reasonable suggestion on what might be happening.
If you still have MCU1, then having cabin overheat protection turned on can cause significantly more energy drop than if you do not have it enabled.
If you parked the car with relatively high SOC, then some owners with older 85 models now experience the battery cooling system running virtually all the time when parked. That's typically at SOC above 80%, but seems to vary based upon the car and battery pack with having seen one owner comment that for them the cooling system stays on when SOC is over 75%.
Can be other possible explanations, but again, need fuller description of the specific circumstances to help provide intelligent guidance.
