I had reported the issue to Github, when I enable sound, the app will crash on iOS devices every time.
I guess that the issue was introduced recently, for it does not exist before I pulled the latest master branch.
How to repeat the issue:
Modify any of the samples codes, enable sound in the engine, build and run, the app will crash.
It reports that 'AudioQueue EXC_BAD_ACCESS', I can not figure it out.