I think that is because some "pages" are really full screen modals. So the back button does take you back to the previous page, but it looks like you went back two pages (closes modal + goes back). I don't spend too much time in the Azure portal but this behavior is rampant in the Entra admin center.
> full screen modals
Thanks. I never imagined this is a thing, it's an useful addition to my mental model of software components, to explain why back button on web behaves in weird ways for some apps.
But it sure does sound like a dumb pattern on the web.