Same thing happened to me - the plug had popped out of the back of the light fixture. Did you replace the trunk lights? If you did and you had to pull on the wiring harness, you might have loosened the taillight connection yourself, it isn't hard to do, sometimes I think cold weather can also cause them to pop out. It's trivial to access them from inside the trunk, I kicked myself afterwards.
Both my rear lights were out, both were unplugged, it was odd. Blinkers flash double-fast to indicate "bulb out" condition (industry standard).
Tesla graciously replaced the left light assembly because it had considerable internal condensation, a known problem.