Hi - was there a resolution to this? I am seeing exactly the same issue. Basic Auth has been set on my collection, everything else is set to inherit from parent, but when I try to use any of the APIs in that collection, I have to go set them manually for Basic Auth.
I have tried replicating this but works fine for me. Here is the example collection link. You can import it and check it out. https://www.getpostman.com/collections/f29db4b0738d820085d5
I have used the Postman echo basic auth endpoint in this.
May I request to know if you have Saved the auth method at the collection level?