Check for any filters that only return if certain conditions are met. I had an issue once where almost all my pages’ content areas were blank. I found the problem was in a snippet of code that looked like this:
add_filter( 'the_content', 'this_will_blank_pages' );
function this_will_blank_pages( $content ) {
if( is_page( 'some-page-title' ) ) {
str_replace( 'some-text', 'other-text', $content );
return $content;
}
}
The problem is that the return $content; only happens on some-page-title, which means that on all other pages, there was no return statement. Thus, blanked content areas.
When I modified my code to this:
add_filter( 'the_content', 'this_will_blank_pages' );
function this_will_blank_pages( $content ) {
if( is_page( 'some-page-title' ) ) {
str_replace( 'some-text', 'other-text', $content );
}
return $content;
}
… it worked as expected. Lesson learned.
Check your theme’s functions.php file and any plugins you might be using for filter functions with that kind of logic.