Hello Hogbinj, Welcome to the Sage ACT! Online Community!
It has been found that having the scheduled sync settings too often can cause this issue. Try increasing the amount of time between syncs to see if this reduces the duplication.
There isn't an automated way to remove the duplicates. You can create a Group, add all of your contacts to the Group - all of the contacts' History items will show in the Group History tab - sort the History tab by Result and delete multiple items at the same time.
While you can create a new database and import the old database into it (retaining contact/company links) - it will also import the duplicated History items. So you would end up right where you started.