I'm surprised this has happened with such a new xc90. I have an 05 xc90 and this has been happening to me in cold weather, or when the xc90 is in colder temps for long periods of time.
What I've been able to find is that there are three possible issues.
1.) Spilled beverages that leak under the gear shift cover can really gunk things up and make the vehicle difficult to shift from park.
2.) The gear selector cable may not be adjusted correctly or may be kinked (if you cab't remove the key from the ignition it may be kinked).
3.) The solinoid that allows the gear selector to release when the brake is pressed may be faulty.
Given your XC90 is still under warranty you should be able to get this repaired at no cost (uness it's the spilled sticky stuff, then it'll be about $100 for the dealer to clean and lube).
I have been removing the surround from the shifter and spraying silicone to help the process along. I do believe it is directly related to the temp outside though. The warmer the inside of the car gets (via sun or HVAC) the less I have this problem.
Good info on this found here