Screen scheme association is the correct option.

Screen scheme association controls which screens are used for create, edit and view operations. If the create screen includes the TrainingPortal custom field but the edit screen uses a different screen that does not include that field then the field will appear on create but not on edit. Administrators set screen associations per project and issue type and a mismatched association is the common cause of this behavior.

Issue security level controls which users can view an entire issue or set of issues rather than which fields appear on specific operation screens. It would not normally make a field show on create but hide on edit.

Field configuration scheme defines settings such as required or hidden for fields across projects and issue types. Those settings apply consistently and do not by themselves cause a field to appear on the create screen and be absent on the edit screen for the same issue type.

Project permissions determine what actions users can take in a project such as creating or editing issues. They do not select which specific fields are included on create or edit screens. The screen configuration controls the visible fields.

Global permissions are site wide rights that grant broad capabilities across the instance. They do not control per operation field visibility on screens and are not the reason a field appears on create but not on edit.

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