I think this is more a configuration related to Auth0's call back url. Worth checking your code in your app and see how the Auth0's return url is generated. My guess is that the app is creating the callback url based on container app's host name rather than the actual frontend url/domain.

this post on auth0 forum seems to have similar issue https://community.auth0.com/t/web-server-behind-gateway-authorization-flow/46060