Changed
Simple oEmbed and oEmbed Providers are installed, with codepen set up.
It's not embedding, possibly due to an api change, or different url for the new codepens.
Could also be caused by incorrect config, or using the wrong modules.
Resources
https://www.drupalarchitect.info/articles/ckeditor-embedded-content
Issues
Simple Embed
Embedded Content
appendXML() does not allow
TODO
Fix or remove modules.
Document embed solutions.