Opportunities not appearing in Marketo

I have a large amount of contacts in SFDC that have an opportunity and have the contact role attached to the opportunity. However, when I go to that contact in Marketo, the opportunity tab does not show any opportunities. I know the Marketo sync user has visibility and access to opportunities because I have other records that have the opportunity tab populated. Does anyone have any insight as to why only some opportunities are syncing over for the contacts?