When opening the UI, the iOS player freeze for a long time and looks like thread deadlock on WriteLock(atomic_compare_exchange_weak_explicit).

Steps:
1. Download the project from ownCloud ("ali-m1.zip")
2. Build for iOS ali-m1/m1_ios/Unity-iPhone.xcodeproj ("reproduce-step.docx")
3. Download and follow instructions (with images) from ownCloud

Result: after exiting the UI player freezes. The music in the background continues to play.

Tested with:
iPhone 6 plus - iOS 8.0 - not reproduced (it never finishes to load. I waited for >25 inutes 2 times)
iPad mini 4 - iOS 9.2.1- not reproduced
iPhone 7 Plus - iOS 10.3.2 - reproduced
iPod 6th gen - iOS 10.2.1 - not reproduced
iPhone 8 Plus - iOS 11.2.5 - not reproduced
iPhone 6 - iOS 10 - reproduced (only when installing for the first time. To reproduce again: delete existing app, install using Xcode again)
iPhone 5S - iOS 9.3.3 - not reproduced