The fix has been moved to acceptance for testing. Be aware that the change is a work-around which let the Workflow execute to the completion, and update the Workflow history, even if the sending of the notification step failed. So the consequence is no more failed WF due to the notification has not been sent.
The root cause – why the notification cannot be sent to a few users, although they have the same setup as whose the function correctly works – is till unknown. (Probably it is a SAP Basis problem).
My preliminary testing succeeded. So, pls, select a WO and trigger WF execution in APB. Unfortunately the symptom in production (notification not sent) cannot be reproduced in APB. So the test should be limited to observe if the WF remains intact and executes correctly. If yes, pls, reply this mail and we can collect endorsements to move to production (… by the next occasion on 28.Oct).