Removed custom field data is kept in Snippet preview

[dariaknl]

How can we reproduce this behavior?

1. Install Advanced Custom Fields plugin and ACF Content Analysis for Yoast SEO.
2. Create Custom Field Group with Custom Field "test field daria" and publish it.
3. Go to Post and fill in "test field daria" with "test content".
4. Update Post.
5. Open Snippet Editor and type in SEO title "%t".
6. Choose from the drop down list "Test field daria (custom field)".
7. Check that in preview "test content" is shown.
8. Update your Post.
9. Navigate to Custom Fields and remove "test field daria" from your Custom Field Group and Update.
10. Go to your Post.

Custom field "test field daria" is not shown in your Post, but

• in Snippet preview in SEO title you still see all data:

• in source the data is still kept:
  <meta property="og:title" content="title test content" />

Expected behavior

In the previous version 7.6.1 this worked in the following way:
after you remove custom field, the Snippet Preview does not keep the data, only cf_custom_field name is shown:

But please note: in 7.6.1 the removed content of custom field is kept on the source!
<meta property="og:title" content="seo title dariadaria" />  

Technical info

• WordPress version: 4.9.6
• Yoast SEO version: 7.7 RC5