The graticle scales so as to be visible with a field of view of 40º and a 1.5x zoomby default. By increasing the default zoom to 2.5x you made it larger in the screen, and as such it went out of what the periscope hole mask lets you see. In other words, your reticle is there but out of the scope circle you see. Return default zoom to 1.5x and you will get it back.
