.well-known/openid-configuration: 0 Unknown Error with Angular ABP client - ABP v5.2.2 #3543

Dear Support,

We recently rebuilt our platform on serverless making use of Aure App Containers (serverless kubernetes managed service).
We have two apps (user web and admin web), user web works but the admin web (the Angular ABP client) does not.
We use Identity Server 4 and the issue is with the discover document.

https://auth.triiyo.io/.well-known/openid-configuration can be visited directly which returns the expected json.
The user web can load the auth server, login and receive a token; no problem.
The admin web (Angular ABP client) redirects to login and receives the following error:

An error has occurred!
Http failure response for https://auth.triiyo.io/.well-known/openid-configuration: 0 Unknown Error

There is a network call failure for that request in the dev tools although the pre-flight works.

Request URL: https://auth.triiyo.io/.well-known/openid-configuration
Referrer Policy: strict-origin-when-cross-origin
:authority: auth.triiyo.io
:method: GET
:path: /.well-known/openid-configuration
:scheme: https
__tenant: xxxx
accept: application/json, text/plain, /
accept-encoding: gzip, deflate, br
accept-language: en
origin: https://demo.triiyo.io
referer: https://demo.triiyo.io/
sec-ch-ua: "Chromium";v="104", " Not A;Brand";v="99", "Microsoft Edge";v="104"
sec-ch-ua-mobile: ?0
sec-ch-ua-platform: "Windows"
sec-fetch-dest: empty
sec-fetch-mode: cors
sec-fetch-site: same-site
user-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/104.0.5112.81 Safari/537.36 Edg/104.0.1293.47

The CORS origins are in the AuthServer appsettings.json as expected:
App.CorsOrigins = has the admin web url (https://.triiyo.io)
App.RedirectAllowedUrls = has the admin web url (https://.triiyo.io)

I have also attempted to explicitly add the sub domain url in but it also fails (wildcards work for the user web client).

Please can you help us resolve this issue, I can provide further information on request.

Regards, Matt

• ABP Framework version: v5.2.2

• UI type: Angular

• DB provider: EF Core

• Tiered (MVC) or Identity Server Separated (Angular): yes