I am a bit surprised at some of the seeming skepticism directed at the OP of this post, though maybe I'm not skeptical because the same thing has happened to me on a couple of occasions. Similar to the situation with the OP. If the car is at a relatively high state of charge, vampire drain is pretty minimal. If it's around or below 20%, it vampire drains pretty fast.
In my case, I parked my car on a Wednesday, knowing the next time I would need the car would not be until Sunday. I was planning to meet up with my friend for lunch and then would charge my car afterwards (for those wondering, I don't have home charging because I live in a condo. I'm allowed to install one, but it's a bit of a pain). I knew I would be driving a total of about 30 miles, so when I left the car on Wednesday with a little over 90 miles, I figured this would be plenty. Unfortunately, by the time I got in the car on Sunday, I was below 50 miles of range left, which basically torpedoed my initial plan. In addition, my Trip odometer, which had efficiency in the 3.5 kwh/mi range when I parked it, had gone down to below 2 kwh/mi. This to me is much more consistent with "battery losing charge at low SOC" than "car bad at guessing mileage". I'm guessing, based on the other posts in this thread, that I might have a bad cell.
Incidentally, something similar also happened to my once in my previous car (Model 3), though that was not at low SOC, it just randomly started vampire draining like crazy. However, my 12V battery also went bad at around that time, so I think that one might have been related to that, rather than a bad cell, being as replacement of the 12V and rebooting of the car seemed to address it.
Anyway, I'm guessing maybe some of the skepticism is related to the fact that if you home charge, you'll basically never see this problem even if you have it. When you can't home charge you are generally much more keenly aware of vampire drain than if you're charging your car on a daily basis.
