Your Audience criteria (i.e., Email Address is Empty) is accurate for identifying people who are anonymous. You might not need SFDC Type = Empty as well along with it.
Chatbot audience criteria used is : Email address = empty & SFDC lead if = empty
Do these known people have the Email Address field populated? If they don't have an email address and are Marketo only person records then it'd make sense for them to see the DC even if they are cookied.
And, yes the Dynamic chat also uses the Munchkin JS, but you need to understand the fact that if a person who's known in your Marketo database visits your website from a new browser/device/clears cookies, Marketo would still consider that person as an Anonymous record as the Munchkin token is no longer associated with their person record in Marketo. Also, yes Marketo will upsert a lead (just like form fills) for people who interact with Dynamic Chat and will not create duplicate person records even if they engage as an anonymous record, i.e., not as a cookied record.
What are other possible scenarios that bot with criteria "email address =empty" will trigger for existing leads.
As said above, the DC would most likely trigger for a known cookied person record w/o the Email Address field populated.
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