Why does the Azure portal not show my Stack for a Web App Slot

Question

I seem to have a strange problem when creating my Web App Slots.

I create a web app like:

az webapp create -n $AppName --plan $AppServicePlanName -g $ResourceGroup --runtime 'dotnet:6' --https-only true --assign-identity

After that is create the slot with:

az webapp deployment slot create -n $AppName -g $ResourceGroup --slot staging --configuration-source $AppName
az webapp identity assign -n $AppName -g $ResourceGroup --slot staging
az webapp config set -n $AppName -g $ResourceGroup --slot staging --net-framework-version v6.0

When I check the WebApp en Slot in the Azure portal. The Stack of the WebApp is set but the Stack of the Slot is not.

I performed this.

az webapp show -n $AppName -g $ResourceGroup --slot staging --query siteConfig

The set the Stack through the portal and performed this.

az webapp show -n $AppName -g $ResourceGroup --slot staging --query siteConfig

Both gave the same result.

I created a few apps this one and some have no problem running the code but one is not starting up, do to the fact that it can't read the Environment settings that are present in the Web App Slot.

What is missing here?