There was an issue an the older version but it look like you are already on 12.2.0, so you should be on the fixed version.
Is this login used to start any other jobs (and is it successfully for the job)? - I trying to understand if the login used has been verify/work for other jobs or if this issues with the same login occurred only for the event.
edit: Just re-read the post and saw you mention it is working for other job and only happen with Event.
Is this running on a linux/unix or window agent? Is the login that it uses the local user on that machine where the job is run, shadow user or if its a LDAP user etc..?
As this is impacting a go-live, I also recommend opening a tick with support as they can work with you more toward a set timeline/sla. (as this was supposed to have been fixed in 12.2.0, they can make sure that it not the same thing that was reported previously).
Additionally, there is a workaround on the KE of the issues that you may consider using until this is resolved.