Hi,
we had this issue two weeks ago and thought it was solved however last week our zaps suddenly stopped working again, because there is something wrong with the way zapier is trying to request the users from JIRA and submitting them back to JIRA. (for instance in the reporter or asignee fields)
It's possible JIRA changed the required format because I've seen similar posts in the JIRA community. (I read on their website that they made some changes to how users are identified, in order to improve user privacy, but that was last year)
This issue might already have been submitted already but I can't find any status on this.
Hope you can help me out or give me an update.
thanks!