Symptoms

No Picking up the Destination users from AD groups
 

Diagnoses

When you have some process instances running which has the Destination users for the events going to a admin AD group. When you add a new person to the group they are not seeing the task in their worklist.
 

Resolution

Once the user is added to a role or group this will not be picked up by K2 straight away. You will have to wait for the cache to refresh which has the default time limit of 8 hours.