didDiscoverCharacteristicsForService not returning CBCharacteristic in iOS11

Prior to iOS 11 we used to get 3 CBCharacteristic from didDiscoverCharacteristicsForService, and we used to use 1 characteristic to WRITE data, but from iOS 11 we are not able to get the 3rd CBCharacteristic to WRITE data. We are still able to get all 3 CBCharacteristics in iOS 10. We read there is a change in coreBluetooth , but we are not able to find anything relavent to this anywhere. Can any Apple Engineer help us please?