The 'associateLead' call is missing the Email attribute. This is required (even though the documentation doesn't call it out).
The valid call looks like this:
mktoMunchkinFunction('associateLead', { Email: 'alpha@beta.com', KeyPositionTitle: 'Software Developer' }, munchkinHash);
(JS reference: https://community.marketo.com/MarketoResource?id=kA650000000Gvx0CAC)