local notification generating multiple notifications at the same time - ios

Question

Sometimes local notification is generating multiple notifications for a single event number is 10. However I'm not getting in testing it's a rare case.
Is there any issue with a particular OS version ??
code is here
-(void)startLocalNotification:(NSDate *)notificationDate startTimeOfShift:(NSString *)startTime {
NSLog(#"startLocalNotification");
NSDateFormatter *newDateFormatter =[[NSDateFormatter alloc]init];
[newDateFormatter setDateFormat:#"dd/MM/yyyy"];
NSString *startDateStr =[newDateFormatter stringFromDate:notificationDate];
NSString *scheduleDateTimeString =[NSString stringWithFormat:#"%# %#:00.000",startDateStr,startTime];
NSLog(#"scheduleDateTimeString :%#",scheduleDateTimeString);
NSDate *setFireDate,*notificationScheduledDateAndTime,*currentDate;
[newDateFormatter setDateFormat:#"dd/MM/yyyy HH:mm:ss.SSS"];
notificationScheduledDateAndTime =[newDateFormatter dateFromString:scheduleDateTimeString];
setFireDate =[notificationScheduledDateAndTime dateByAddingTimeInterval:-60*15];
currentDate =[NSDate date];
// NSTimeInterval distanceBetweenDates = [notificationScheduledDateAndTime timeIntervalSinceDate:[NSDate date]];
// NSLog(#"distanceBetweenDates :%f",distanceBetweenDates);
NSLog(#"Current Date :%# setFireDate :%#",currentDate,setFireDate);
if(counts > 15){
doNotShowNotificationAlert = NO;
}
switch ([currentDate compare:setFireDate]){
case NSOrderedAscending: {
NSLog(#"NSOrderedAscending");
}
case NSOrderedSame: {
NSLog(#"NSOrderedSame");
if(doNotShowNotificationAlert == NO){
notification = [[UILocalNotification alloc] init];
notification.fireDate = setFireDate;
NSLog(#"setFireDate :%#",setFireDate);
notification.alertBody = #"Shift Start Alert!! 15 mins to go.";
notification.timeZone = [NSTimeZone defaultTimeZone];
notification.soundName = UILocalNotificationDefaultSoundName;
NSDictionary *infoDict = [NSDictionary dictionaryWithObject:#"100" forKey:#"notificationID"];
notification.userInfo = infoDict;
[[UIApplication sharedApplication] scheduleLocalNotification:notification];
NSLog(#"info Dict :%#",infoDict);
doNotShowNotificationAlert = YES;
}
break;
}
case NSOrderedDescending: {
NSLog(#"NSOrderedDescending");
break;
}
}
}