Can you confirm you are using WordPress 4.9.8 as well as Yoast SEO for WordPress 8.3?
Could you please try and perform a conflict check first as we’re not familiar of any known issues that could cause the plugin to add content to your paragraphs.
1. Make sure the issue doesn’t persist when Yoast SEO is disabled.
2. Check for conflicts.
3. Check for JavaScript errors with your console.
If you find any JavaScript errors related to Yoast SEO or if there is a conflict with a plugin or a theme, you can create a new GitHub issue for our developers. Please report the issue to a third party developer as well.
If you didn’t find any conflicts or errors, we think the issue is specific to your site. We’d need to investigate further but are unable to do so on these forums. You can purchase Yoast SEO Premium and receive our Premium email support and we can help you further.