This sounds as though it's related to the problem that I reported in this thread ...
... and in this bug ...
While the thing that triggers the problem is different, the problem (audio dies) and the workaround (go to sleep mode, then return) are the same.
I assume that this is a bug in AIR or, more precisely, there's some new requirement in iOS that AIR needs to accommodate. Adobe has reproduced the problem on their end (see comment in Tracker), and I assume that fixing this will be a fairly high priority for them, as sound is ... um ... kind of important.
I suggest that you either create a new bug in the Tracker and link it to mine, or simply add a comment to my bug explaining that one can also cause the same problem by playing a video.
Thanks for your reply.
I tried to test the program using AIR 25 on iOS 10.2.x and this problem didn't happen. It only happened when the program use the AIR 26. So I think this is something more related to using WKWebView for StageWebView on iOS in AIR 26.
Thanks for reporting the issue. We are investigating it.
Adobe AIR Team