Outlook 2016 - Preparing items for tracking

Hi all,

I have a single user in my organization who is having problems with Outlook 2016 connecting to Dynamics 2016 (on prem).

When synchronizing, I just get the page with an active task of "Preparing items for tracking" and I get no further progression despite literal day of waiting.

I've got logging turned on and all I can see in the logs is constant alternating calls which result in "Acquired lock on orgID: {GUID}" and Call to IsOrgOggline succeeded.

Does anyone have any ideas how to progress further?

Regards.