Yeah I'm a little surprised this wasn't worked out before the launch of the pro. Devs esp as big as Spotify can usually get their hands on new devices earlier than others for testing their apps....
When I first got the iPad pro set up with an iPad backup the old version of Spotify opened and worked perfectly. Then I did app updates and now experience the same issue. Hope it's fixed soon.
It is absolutely ridiculous, in fact, the overwhelming amount of issues can be fleshed out in the simulator, especially given that the majority of differences for an app like Spotify will involve UIDevice and screen size queries, which can be done in the simulator to add support for the larger screen size. My hunch based on the crash & the trace I have seen of the crash on my device is this is exactly it, the old app made an "unsafe" screen size call in setting up UI bounds or frames and no one even bothered launching the app in even the iPad Pro simulator, let alone on a real device. There really is no excuse for this bug to have made it to launch day.
This is now fixed, with Spotify for iOS Version 4.4.0: