SharePoint 2013 'Sync to outlook' problems (not working)

Trying to get the 'Sync to Outlook' working for a list.

Our Environment is SharePoint 2013 Enterprise with Exchange 2013

I have Mysites (One Drive) up and running, Search, and profile sync.  All that seems to be working with no problems.

However I have an issue when I try to turn on 'Sync to Outlook' on a list.

After I turn it on I get this when checking the status "Sync disabled due to errors"

If i watch the ULS logs i see this error.

Couldn't find a user using property 'SPS-UserPrincipalName' of value 'myusername@our.domain'

I found a similar issue on here but i cannot figure out how they solved the problem.
https://social.technet.microsoft.com/Forums/office/en-US/d5654a76-d2e5-46d8-81b9-ce4a477cc271/search-alert-issue?forum=sharepointsearch

Any help on this would be appreciated!