Same issue arrived in all of my client's site,
Temporary solution is below
1. Open class-sitemaps.php under wp-content/plugins/wordpress-seo/inc/class-sitemaps.php
2. Go to line no 305 and change code like below
$caching = apply_filters( 'wpseo_enable_xml_sitemap_transient_caching', false );
Thats it, and it will fix the problem, but next time when Yoast SEO release update and you update, it will flush these changes!