When I add locale to URL the application requires login

[DanielChristensen1]

Hello,

I have a custom web application that I'm working on.

It is based heavily on the boilerplate from: configurable-app-examples-4x-js/webmap-ts at master · Esri/configurable-app-examples-4x-js · GitHub 

Besides that it has a custom layer control widget.

When I load the app it works fine. But as soon as I add "&locale=en", it prompts for login to the portal.

Can anyone explain to me why, or what I can do about it?

[DanielChristensen1]

Apparently if I click cancel several times I can get to the application again.

The console shows the following:

Note:when loading without locale defined it shows:

Notice the difference in language. For some reason it seems to ask for login when the locale is not danish (my default browser local), while just accepting that items are inaccessible if the locale if default danish. 

Maybe this can help someone explain to me why this is happening. 

[DanielChristensen1]

Apparently it's related to the default basemap group.

When I create a group in the Portal for basemaps, the application no longer requires login when locale is set.