Symptoms

When passing the AAD UPN, the workspace says it was assigned to their AD worklist, but it does not appear in their AD or AAD worklist.

Diagnoses

The hybrid set up of AAD and AD and when passing an AAD UPN (which is effectively an email) to K2 it's not entirely sure what to do with it has two separate User Management Services to work with, both of which contain that email (assuming Dirsync or someother such tool). Effectively K2 is not sure what to do with the task, it needs specification.

Resolution

Rather than using the UPN use the FQDN instead. The security label is specific and tells K2 exactly where the task ought to be assigned.

This white paper offers good insights on hybrid authentication
http://help.k2.com/kb001746