How do I prevent CKEditor 4 from stripping Google AdSense asynchronous tags?
Have you read this blogpost (not by me) Drupal WYSYWG Module Custom CkEditor Configuration by Philip Norton.

Your &lt;script&gt; tags are not being stripped out, but the funky &lt;ins&gt; tag is. From that blog post you should be able to add a protectedSource to the AFC rules so that those elements are not stripped. This is untested but deriving from the blogpost:

// Allow Google Adsense &lt;ins&gt; tags, I'm being more specific
// than allowing any raw &lt;ins&gt; tag here. This may be too specific, but
// play with it.
config.protectedSource.push( /&lt;ins class=\"adsbygoogle\"\&gt;.*?&lt;\/ins\&gt;/g );


In order for this configuration to work you may have to install the WYSIWYG module (or append to your own ckeditor javascript profile directly).