Page Builder is Missing
The most common cause of this issue is for sites using a custom domain. Before mapping a custom domain, you would have wanted to log into your Website Builder site to access your Page Builder tools using the default domain:
Example URL sitename.teamsnapsites.com/wp-admin
Once you have a custom domain, you will need to log in at that custom domain in order to access your Page Builder tools:
Example URL customsitename.com/wp-admin
If you are logged in to Website Builder, but Page Builder isn't launching for you, try logging out, clearing your browser cache, and then log back in at your custom domain + /wp-admin/ and you should be good to go!