This just happened to my Model 3 on a weekend trip to my brother-in-law's place. I'm doing my usual early morning work on my laptop in the living room during some moderate rain. I kept seeing headlights flash about every minute or two without a car driving by, So I stared off into the driveway, and it was my Model 3 flashing the headlights every few minutes. I shut off sentry mode from my phone and it stopped. With the additional sentry activity and only a 10 degree temperature drop, range is reporting down over 15 miles since parking last night.
It'll be interesting to see how many events occurred once I get out there. Thanks Google for finding this thread immediately when looking up this problem.