Hi,

This is Tim with Microsoft Office 365 SharePoint Support.

Unfortunately, this is a normal error if you just switched to your custom domain and then try to edit your website. There is a propagation period before everything will be available to use with your custom domain. Please try again tomorrow and let me know if you are still seeing the issue.

I will continue to monitor this thread and wait for your reply.

Thanks,

Tim Muth

Microsoft Office 365 SharePoint Support