Exchange not syncing with Contacts App (Big Sur)

**Symptoms:** I've got a user with 3,051 contacts in his exchange account. We use exchange online. He is able to see and sync his contacts with the Outlook app and his iPhone (running latest iOS, 14 I think?). He has had this issue for over 6 months now on multiple computers and multiple OS versions, all Macs. Specifically, when we add his exchange account to the Contacts app, either they never sync, or a fraction of them sync. (On macOS 10.12 he gets 900 of them, on macOS 11 he gets 0) **Goal:** My user wants his contacts to appear in Contacts, because he uses the Messages app to text, and wants to see who is messaging him. This is a corporate account so we want to keep all the contacts in Exchange unless we have no other options. **I've tried:** 1. Adding and removing the account. 2. Moving all contacts into a folder. (This worked last year but not anymore) 3. Creating a new contact in multiple places to see if it syncs. If I make it in Contacts it syncs. If I make it anywhere else, nothing. **Question(s):** 1. Is there a way to check the sync status of Contacts within the Contacts app? 2. Failing #1, is there a log somewhere I can look at with details about the sync process? 3. Failing #1 and #2, are there other tools out there we can use as an intermediary between Contacts and his Exchange account?