This is my take on the situation using the information directly from Tesla.
http://ir.tesla.com/static-files/1b240f1e-b519-4b40-b14b-fea44698c3af
The Q1 update letter states that as of the end of Q1 (March 31) "Net Reservations exceeded 450,000". "Net Reservations" is a confusing figure because it includes what you would typically think of as a reservation, BUT it also includes someone who has reserved, has configured, and is awaiting delivery of their car.
With the Q2 delivery report update:
Tesla Q2 2018 Vehicle Production and Deliveries | Tesla, Inc.
Tesla stated that the "Net Reservation" figure was now "roughly 420,000". Using these two data points we can see that during Q2 "Net Reservations" declined by about 30,000 give or take over those 3 months. Remember though that DURING Q2 Tesla delivered 18440 Model 3s. Every single one of those model 3s was delivered to SOMEONE who had a reservation at the end of Q1, a configured order is still counted as a "Net Reservation" whereas a delivery eliminates a "Net Reservation".
So if we take the total decline in the "Net Reservation" figure over the period which was 30,000, and back out the deliveries of 18440. We are still left with a decline of around 12,000. This decline cannot be explained by deliveries. This 12,000 decline is explained by existing reservation holders cancelling faster than new reservations were coming into the system over the 3 month period. Absolute value of cancellations > absolute value of NEW reservations during Q2.
So the question is what is going to happen going forward. Tesla is currently pulling the demand levers to reverse that relationship, they need absolute value of new orders (since there are no more "reservations" someone who configures and orders a model 3 today but does not receive delivery is still a "Net Reservation") > absolute value of cancellations.
This is definitely something to keep an eye on going forward, I hope the provide an update to the "Net Reservation" figure in two weeks because that could add a lot of color to what is going on behind the scenes.