The elements that stiffen a panel at the edges do not represent stiffeners in the sense of a stiffened plate according to EN 1993‑1‑5 [1], Section 4.5. If the limits of the panel are defined as stiffeners, the message shown in Image 01 appears. It is necessary to delete these stiffeners.
The panel shown in Image 02 includes Elements 1 through 3 and Stiffeners 1 through 4. However, Stiffener 3 and Stiffener 4 are located at the edge of the panel (marked in red in Image 03), so the message shown in Image 01 is displayed. It is necessary to delete these stiffeners (Image 04). This is also shown in the video.