For some odd reason the main slot of the #Azure App Service was using the v1 issuer endpoint of #AzureAD, while the other slots were set to use the v2 issuer endpoint of #AAD.
I didn't know that #AzureAppService slots can use different auth settings. TIL.
Also, it is still not clear why would `/.auth/refresh` only work with v1 and not v2, or put it better, why did v2 stop working on 2022/11/02 ?! #AzureSupport
Anyways, v1 works and that is what's important!