Im experiencing the same very difficult to figure out and work around IOS bug. I may have some insight. Heres a capx http://tiny.cc/nqstfx
demo link below.
Using the latest stable c2 release. Tested on ipad 7.0.4 and ipad mini 7.1. Also tested in numerous ios versions/devices in emulators. Cannot replicate in emulators.
Steps to reproduce...
1. close safari
2. clear cache
3. visit http://tiny.cc/25rtfx
4. touch anywhere to trigger sound and play animation of thrown object.
5. hit the red box with the object (sprite animation) to trigger collision sound
6. refresh and retry a few times. The impact sound eventually stops working. Throwing sound continues to work.
Important insight :
In testing it seemed best to setup the throwing sound to be in the 'music' folder in c2 and triggered on touch.
The collision sound is in the 'sound' folder in c2 and triggered on object (sprite animation) collision with red box (sprite).
It is only the sounds from the 'sound' folder that stop playing.
So far removing the contents of the offline apache cache file seems to resolve the issue. Further testing required.
No cache version here... http://tiny.cc/h5stfx
Clearing cache a few times and possibly closing browser eventually makes it work again. Highly unpredictable.