Symptoms

K2 roles are not updated, e.g. a user has been added into K2 role very long time ago but new process instances which using this role do not reflect the change as the newly added user is not able to receive any tasks.
 

Diagnoses

First of all you should try manually refresh affected role via Workspace:

1. Go to Workspace > Management Console
2. Expand Workflow Server
3. Go to the process which uses the Role in question (Processes > eYour Process] > Roles)
4. Select the Role in question and click on Refresh
5. Try and start a new instance to see if this grabs the updated users

Alternatively you can try the force identity refresh script can be executed to resolve this:
 

1. Run the force refresh script:

UPDATE cIdentity].cIdentity]

SET "ExpireOn] = GETDATE()

,=Resolved] = 0

,eContainersResolved] = 0

,lContainersExpireOn] = GETDATE()

,yMembersResolved] = 0

,tMembersExpireOn] = GETDATE()

WHERE Name = 'Role Name'

2. Perform K2 service restart

Resolution

Try to manually refreshed the role via Workspace or execute identity refresh script (see details above). Though both approached supposed to bring the same result in certain scenarious it may work only after manual role refres in Workspace GUI, but not after use of force identity refresh SQL script.