Contacts Sync to Outlook (server side sync) not working for one user

Hello everyone,

we set our CRM to server side snyc (we use Office 365). For me all the 200 contacts are synced to my exchange / outlook. The sync setting is set to - all active contacts -.

For my collegue - with the same settings (all active contacts) - somehow only 75 contacts are synced.

We have CRM for Outlook installed. 

Do you know what could be wrong that not all active contacts are synced to his exchange?

Thank you

Markus