WordPress 4.3 Changes in Template Hierarchy

In WordPress  4.3 there is a new template file added in theme template hierarchy called singular.php . This will allow theme authors to use a common template for any singular post type.

It follows the rules of is_singular() and comes after single-{post-type}.php, single-post.php, single.php, andpage.php.

Template hierarchy for singular post types
Template hierarchy for singular post types

To learn more about WordPress theme template heirarchy : https://developer.wordpress.org/themes/basics/template-hierarchy/

Automatic update of Child Theme to Parent Theme

After automatic update of child theme to parent theme, During update we just update code of theme, but what about WordPress, WordPress still assuming current theme as child theme.

When you activate child theme, there are mainly two site options template and stylesheet who store parent theme and child theme slug. After updating you have to update that site option also (There are others relative options also).

Add following code into your theme function.php

if ( is_child_theme() && 'current-theme-slug' != get_template() ) {
    switch_theme( get_stylesheet() );
}