Hey Brian, sorry to hear you're having trouble with this! First, the error itself seems to point towards a connectivity issue, or problem resolving one of the properties in the profile. Since the user's account has been syncing prior to this though I'm leaning on a property issue in the Outlook profile. Can you try doing a full resync of this user's account on a fresh Outlook profile to see if the issue persists there? Those steps are outlined here: 

The more important steps though are creating a new profile in Outlook, removing the sync keys in SmarterMail under Settings>Connectivity>Synchronized Devices (only the MAPI ones), then adding the account once more in the new Outlook profile. That should force it to pull down a fresh copy of the data from the server and eliminate anything that is problematic in the old profile. 

If that works the user can likely just continue using the new profile for best results, but you may also be able to correct the issue on the old profile by running an OST repair on it in Outlook. If that doesn't resolve the issue, the user's PC might have trouble reaching one of the autodiscover components it requires for MAPI connectivity. Those requirements are:

If any of the above items fail from the user's PC, or from the internet (where the O365 servers are testing from) this will ultimately lead to connectivity issues while adding or syncing the account so they are worth checking for sure. Let us know what you find out and please don't hesitate to submit a ticket if you need a hand. 

Hi Brian,

A support ticket has been started to help diagnose this issue directly. 

I did nothing and it started working... there didn't seem to be any other connectivity issues... so who knows.