Page Builder is Missing
The most common cause of this issue is for sites using a custom domain. Typically, you'll log into your website builder site using the default URL:
Example URL sitename.teamsnapsites.com/wp-admin
Once you have a custom domain set up you'll need to begin logging in using your custom domain:
Example URL customsitename.com/wp-admin
Give that a try and you should be able to access page builder again!