Reports of in-app purchases not working - ios

Question

Our company is receiving many reports of in-app purchases and in-app purchase restores not doing anything. Most reports mention that no action occurs within the app when the purchase completes, or when the restore button is tapped.
All of our sandbox and live app testing shows that the IAP feature is working flawlessly. Further, the vast majority of our users report no issues with the feature. Still, it's odd that such a large number of users are reporting a problem.
We recently had to rebuild our .xcodeproj file from scratch, after losing the prior copy, but all of the other files remained unchanged. Could this have somehow caused the problem?
Per the debug information provided with our reports, the issue appears to affect nearly every device and every iOS version. The only common thread is that it's affecting the versions of our app produced after we rebuilt the Xcode project file.
This is more of a high-level question to see if others are facing or have faced this issue. Because of this, and because the code appears to working fine, no code has been provided, but please let me know if specific code examples would be useful.
Per comment below, here is some relevant code relating to the restore process:
- (void)restoreCompletedTransactions {
[[SKPaymentQueue defaultQueue] restoreCompletedTransactions];
}
- (void)restoreTransaction:(SKPaymentTransaction *)transaction {
NSString *product_identifier = transaction.originalTransaction.payment.productIdentifier;
if(product_identifier == nil)
product_identifier = #"PRODUCT_IDENTIFIER";
[self provideContentForProductIdentifier:product_identifier];
[[SKPaymentQueue defaultQueue] finishTransaction:transaction];
}

Answer 1

There is an issue on App purchase restoring from iOS 9.0.
Use this bunch of code for restoring.
- (void)restoreCompletedTransactions {
[[SKPaymentQueue defaultQueue] addTransactionObserver:[yourclass sharedHelper]]; // Yourclass can be self, or can be where did you initialise your helper.
[[SKPaymentQueue defaultQueue] restoreCompletedTransactions];
}