How do I turn the system volume overlay back on after using MPVolumeView?
This is sadly an issue with the private framework in the earlier versions of iOS.
I understand your wish to make a solution for this, but it would cause your code to manipulate the private framework, making your app unable to pass approval.
Fortunately, the version span that had this error is short, and the number of devices in circulation with these version are growing thinner by the minute.