When add the "Additional Assignees" field, I still can't see this filed in story when open to edit the story, and in configure I am selecting "All".
You field needs to belong to the Edit and potentially the View screen of the Screen Scheme used by your project.
I would recommend to make sure that the field is in these screens that you can access from your Project Parameters => Screen scheme
Let me know if it helped,
Connect with like-minded Atlassian users at free events near you!Find an event
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no Community Events near you at the moment.Host an event
You're one step closer to meeting fellow Atlassian users at your local event. Learn more about Community Events