After upgrading to use the vanity URLs instead of the KUID URL, you are unable to access the Designer & Management pages for K2 Cloud. The error below appears:
"An error occurred trying to process the request. An error occurred while processing a WS-Federation sign-in request"
As a temporary workaround you can access the site using your instead of your environments URL as per example below:
After this you should be able to get into the site. Do the same for Designer as well.
This should be done in Incognito mode, after performing these actions you should be able to get into your site with the original vanity URL.