HI ! Look at to the material view picture, there is everything ok, then look at rendered picture where i marked, there is wrong thing happenin’ like i did this.If you look carefully you will se there some wrong triangles . You can see whats right in material view picture.Why it happens as it ?
Have you recalculated normals?
Ow. No , how ?
I just clicked to recalculate
Check your modifier settings, it looks like there is a solidify modifier which only shows in rendered mode.
Check Y position of your vertices. Position of top vertices different than bottom vertices.
That topic is from May…
But not closed. Maybe another one meet same problem.