White smoke and coolant loss

[didgeridoo]

Hello, I bought a 2019 crosstrek after leasing it for 3 years. The car is at 50k miles currently, runs and drives great. I maintained every oil change at 3k miles, and swapped all fluids about 10k miles ago. About 2 weeks ago it started puffing white smoke upon startup for about 3-5 seconds. I took it into the dealership where they've had it for 4 days only to tell me they cannot recreate the issue and that my car is perfectly fine. When I asked about the coolant dropping they told me it could be a possible head gasket leak. I literally signed the paperwork to buy the car 2 weeks ago right before this started happening. Any help would be appreciated.

 

[Ecmbuster]

Have them pressure test the cooling system.
Have them attach a pressure transducer to the coolant tank and measure pressure pulses from the combustion chamber into the cooling system.
Those tests will define the answer to your question.