On Galaxy 6S, only some Contacts sync with Active Exchange. Help?

[AC Question]

My boss is a power user and heavily relies on Outlook on her notebook. We use Office 365 Small Business as our company Exchange server. She's been using her Galaxy 6S to sync with her Exchange account just fine - Mail, Calendar, Contacts, and Tasks. She has 8000 contacts. Then last weekend out of nowhere the Contacts disappeared from the phone although they are still on the server and available in Outlook. She took the phone to where she bought it and they couldn't resolve the issue. We removed the Active Exchange account and recreated the account. It syncs mail and calendar just fine, but weirdly it only synced about 600 Contacts. What about the other 7400?

I'm out of my depth here. Help would be much appreciated!