This happens because the same field is used in another view too, and someone had set a required condition there tied to a visibility condition that never actually shows on screen. So even though your current view has no required or visibility condition, Pega still marks the field as required because of that other hidden view. Check every view in your flow that uses this same field, and find the one where a required condition is tied to its visibility condition. Remove that required condition from the other view, and the validation error will stop appearing when you submit the case.