When trying to edit the sitemap by opening it in the systemsolution it fails with following message:

(English: An error occurred. Please try again or contact your system administrator if error persists.)

I'm running an on-premise IFD configuration. The error only appears when opening the CRM with internal URL (e.g. https://internalcrm.contoso.com/MyOrganization) When doing the same by using the external URL (e.g. https://myorganization.contoso.com) it works fine. Fiddler tells me that the required organization name is missing for some API calls when opening the designer by internal URL:

"internalcrm found in request URL: internalcrm.contoso.com/.../ is invalid. Expected organization name: myorganization"

As you can see it tries to use "internalcrm" as the organization name instead of the right one "myorganization". Does anyone have an explaination for this behavior?