Hi Muhammed,
If you get this problem only with this element, then what is shown in the screenshot is that the model is made up of several elements under a Null Object named Device. I don’t know, but the model may have splines at each edge, as is the case with models imported from other programs especially imported from Sketchup, so when you select the Null Object, you will see in the viewport that all edges are activated, even in Gouraud Shading mode, so you have to delete the splines; If my guess is wrong, please post the model file here to let me check it for you.
Thanks!