Galaxy S6 :: Contacts Don't Show Up At All

I purchased the S6 back when it launched and haven't regretted the decision once. However, I've had this issue for around a month and a half whereby quite a few contacts don't show up - at all - they used to, but have vanished. Outlook thinks they're on the phone, but the phone won't show them Many people call or message me, but their number doesn't show up.

I currently use outlook for synchronising between three phones and a tablet. The tablet and other two phones display all contacts, but this S6 however doesn't - bearing in mind the tablet is also a Samsung.

I've tried wiping the contacts and then putting them back again through outlook, but still no change.I've also checked the display settings found within the contacts app to ensure it's not selected on something whereby it doesn't show all contacts.