Thanks for your posting. The issue is likely that you haven’t activated TestRail’s background task on the server yet. The background task is mostly responsible for computing TestRail’s reports as well as processing email notifications but also for adding custom fields in the background.
You can verify the status of the background task under Administration > Overview. You can learn more about activating the background task here:
You can also clear the email queue before activating the background task via the little link on the administration overview page, next to the queue background task’s status (this prevents any queued emails to be processed, which could be hundreds of emails or more).
I hope this helps!