I am an admin, Jira Cloud. I can assign myself to an issue in the Assignee field, but I can't assign myself in any other UserPicker field (multiple users) that I create.
Why I need this:
When a QA starts working on an issue after the assigned developer is done, it is critical for me that the Assignee remains the same. I created a UserPicker field "Members" for other people involved to be stated there, and I noticed that I can't pick myself in that field, my name is not on the list.