Template attributes disappear on designated posts page

WordPress Theme: Oxygen. I am using the default page template for most pages but when I designate the posts page the attributes of the template, ie: banner, sidebars, custom menu and custom background, disappear. I assume there to be something obvious that I’m overlooking. I’ve tried different templates but none of them appear unless I turn off the posts page allocation in settings. Surely a posts page can be attributed a page template? Not come across this before. I am using a Child Theme for the first time so maybe the error is in that?