Issues syncing with Exchange accross multiple users

[congo pillage]

I support users that share an Office 365 mailbox, and have been fighting sync issues for months. There are 12 users that all access the same email address and have it synced with Outlook 2016 on their individual machines. Once they add a second, individual account, sync starts going a little nuts. They will be unable to move items across folders, search individual mailboxes, save changes to the shared calendar, and other sync related issues.

The 'Sync Issues' folder currently has about 33000 messages, most are for the folder 'Recipient Cache' and look like;

11:28:49 Synchronizer Version 16.0.11629

11:28:49 Synchronizing Mailbox 'XXXXXXXXX'

11:28:49 Synchronizing local changes in folder 'Recipient Cache'

11:28:49 Uploading to server 'https://outlook.office365.com/mapi/emsmdb/?MailboxId=60ab9620-dc'

11:28:52 2 item(s) updated in online folder

11:28:52 Downloading from server 'https://outlook.office365.com/mapi/emsmdb/?MailboxId=60ab9620-dc'

11:28:52 Error synchronizing folder

11:28:52 [80040109-50A-80040109-560]

11:28:52 The function cannot be performed because the message has been changed.

11:28:52 Microsoft Exchange Information Store

11:28:52 For more information on this failure, click the URL below:

11:28:52

11:28:52 Done


Any insight on how to proceed in troubleshooting is greatly appreciated. Please let me know if more information will help provide a solution.

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