Why doesn’t the Video SEO plugin index all my videos?
As of Yoast SEO 20.0, the settings interface inside our plugins has received a major overhaul. Please update to the latest version of Yoast SEO if your plugin does not look like the screenshots you encounter in our Help center.
The Cause
Especially on websites with a large number of videos, the plugin can have problems finding all the videos, due to (a shortage of) memory.
The Solution
You should try going to SEO-Video and then re-indexing a number of times. You may need to scroll down to find this feature. However, be sure to leave the ‘Force Re-Index’ box unchecked. Once the number in the sitemap is static, it has found all the videos.