Data not pulling through from Salesforce Custom Object

[Fiona_Evans]

I have successfully pulled through Custom Salesforce objects to Marketo in the past, but I seem to having a problem with one particular object called Interactions.We have quite a customised salesforce and this object records all emails, meetings etc with contacts. It also cross references the Account object. It looks like the below:

The Contact object is the Parent object, but there is also an Interaction Reference object that links the two.

I have enabled the sync on the Interaction reference object and the interaction object.

However when I go to a smart list with the filter 'Has interaction' it is pulling through zero people, although nearly everyone on our database has an interaction against them. I have tried to follow the Marketo documentation through but cannot think why this data isn't showing as expected. Is there something obvious I've missed?

Help much appreciated!