iOS 9 causes sound problems with various apps and games. iOS musicians – tread carefully

iOS 9 seems to be stable so far, with no massive usage breaking bugs reported by users, but with as many apps as there are in the App store, it was only a matter of time until unpredictable issues started to pop up. Apparently, Apple's tinkering with the mobile operating system caused some apps' and games' sounds to go haywire.
Another issue — and this one is a bit more serious for those who use their iPads for audio production — Positive Grid's “Bias Amp” and “Bias FX” guitar processing apps have begun introducing hiss and pop effects when users have both Stereo Mode and Ultra Low Latency modes on, or when effects such as the octaver are on. The issue has been reported by users that are on the iPad Air 2 – pretty much the best iPad you can get right now. The app developer hasn't replied to the issue report thread, but we have to assume a fix is in the works. For now, iOS-using musicians should tread carefully and read user reports about the various apps, before taking the plunge and updating.
A smaller percentage of users have reported that their notifications are not producing any sounds. The suggested fixes for this issue vary from hard-resetting the iDevice (hold home button and power button until it restarts), to muting notifications and restarting, simply disabling and re-enabling Bluetooth, and resetting Network Settings.
Have you noticed sounds going haywire on your iDevice, after updating to iOS 9? Let us know what else there is to look out for.
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