Error: Missing required field "entry-title"

I am using Spacious theme and I am getting Error: Missing required field “entry-title” error.

Most of people in forums tell to add

<h1 class="entry-title"><?php the_title(); ?></h1> in content.php.

but in my case, content.php already has

if( !is_single() ) {

	?>

	<header class="entry-header">

	<h1 class="entry-title">

		<a href="<?php the_permalink(); ?>" title="<?php the_title_attribute();?>"><?php the_title(); ?></a>

	</h1><!-- .entry-title -->

	</header>

	<?php

	}

	?>

Please help to resolve the issue.