For my JIRA Next-Gen project, I've organized my project into Epics with a collection of child issues. At the Epic level, I have a custom field (People) labeled "CMS Specialist" where I designate a specific individual.
I'm trying to create an automation where, once the issue is transitioned to a specific status ("Content Load in Progress"), the issue is auto assigned to the CMS Specialist designated in the field mentioned above.

I'm trying to use the smart value {{issue.epic.CMS Specialist}} to pull from the parent epic and set the assignee for the task, but every time I test this, it fails. Audit log shows the following error message:
"Specified user does not exist or you do not have required permissions"
The weird thing is that it occasionally works for a (very) small group of users, but not most. I have administrator permissions for my board, so I don't think it's a permissions issue. I also tried making sure that the smart field was correct by creating a new automation that set the description to the {{issue.epic.CMS Specialist}} field, and that worked correctly. It returns the following in the description field on trigger:
{self=https://sbd-appsvcs-ebiz.atlassian.net/rest/api/2/user?accountId=xxxxxxxxxxxxxxx, accountId=xxxxxxxx, avatarUrls={48x48=https://avatar-management--avatars.us-west-2.prod.public.atl-paas.net/xxxxxxxxxx, 24x24=https://avatar-management--avatars.us-west-2.prod.public.atl-paas.net/xxxxxxxxxxxx, 16x16=https://avatar-management--avatars.us-west-2.prod.public.atl-paas.net/xxxxxxxxxxxxx, 32x32=https://avatar-management--avatars.us-west-2.prod.public.atl-paas.net/xxxxxxxxxx}, displayName=xxxxxxx, active=true, timeZone=America/New_York, accountType=atlassian}
I've x'ed out the person's name and id in the example above, but it's the correct person.
Any ideas?