I had been using Wwise 2015.1.65, which worked OK under iOS 11 although there were some issues. My AAC sounds played fine.
I just updated to v2016.2.4 build 6098, and now my AAC sounds don't play at all on an iOS 11 device
AK Error: AAC decoder failure: 205100711
AK Error: Failed creating source: 205100711
I no longer have an explicit codec registration (I do include <AK/Plugin/AkAACFactory.h>), but was hearing AAC sounds just fine on an iOS 9 device. And non-compressed sounds are OK on both.
Is this a known issue? Did I miss some trick in migrating?