TL;DR. I accidentally used my old nickname when I created my Atlassian account.
I created a question in the Atlassian community.
Then I discovered that I had used the wrong "Public Name" (when creating the Atlassian account) and changed it to the correct one using "Edit in Atlassian account".
However, when I checked the page with my already created question, the "Public Name" had not been changed.