Did you solve it? Im having the same issue.
After some investigation I found thar CRM is suppose to sync:
- Task to any partner related
-Activities to the partners wich relationship on category function is BUR011.
This is an issue on my scenario and I need to skip some of them.
Im searching for badis but the ones availables on the Spro look like only relvenant for Outlook->CRM sync
When i need the CRM->Outlook
Im having a look on class CL_CRM_XML_GW_SYNC
But still not certain.
Regards