In Vuforia 9.4.6, there waas a different error:
targetFinder->startRecognition() was crashing. Now, with 9.6.3 that seems to be working fine again, but when we call
finder->enableTracking(*cloudRecoResult), it crashes (every time).
Our code is the same it's been working for the past year, based on: https://library.vuforia.com/articles/Solution/How-To-Implement-Cloud-Reco.html (C++ version). Same code is working fine in Android, so this is definitely an issue within iOS SDK.