Why am I getting this line when Preview even it was not in Design

[Dennis_N]

The infamous thin black line during presentation mode

That’s a sub pixel rendering issue where the background shines through I would say and it can be avoided by avoiding subbixels and using 100% view. You can also group elements and give the group or frame the same color as the elements so the background color of your page does not shine through. Non the less I agree this is totally annoying and should not be like this.