Hello,
I believe it is a bug since I have already done that same task for another app I have created and it worked perfectly.
When I try to add my app on the home screen of my IPhone, the icon displayed is a screenshot of the app page instead of my app icon.
Like @eltintero mentioned, I’ve found that the icon eventually loads if you wait a minute or so after pressing “add to home screen” but before hitting “add”.
I have the same issue on the home screen app icon. It worked fine on the first one then the second app - basically duplication of the first, it doesn’t work. It shows the icon then overlays with a screenshot.