We have enabled Campaign Influence in our org, and it seems to be working correctly. But looking at a Campaign Influence report, it appears that about 20% of Campaign Influences do not seem to have a Contact.
My understanding is that Campaign Influences are created when
a Lead which is a CampaignMember is converted to a Contact and an Opportunity, in which case the converted Lead becomes the Contact in the Campaign Influence record
a contact role which is a CampaignMember is added to an Opportunity, in which case the Contact becomes the Contact in the Campaign Influence record.
So how does our org have so many Campaign Influences without Contacts?