RBR850 Web User Interface no longer requires a password to access

I think I have vague idea of what is going on.

So first off, clearing cache and cookies did not do anything.

I tried with the Edge browser (My main browser is Chrome), and that did work correctly: was prompted for login.  And after clicking logout and trying again, was prompted for login again.

I realized that I have Google Sync turned on in my Chrome environment.  So I opened a new browser window under a guest profile and this time I was correctly prompted for login, and clicking logout also worked correctly, forcing me to need to login again.

So I'm guessing that there is something with Google Sync that is somehow over-aggressively preserving my credentials (it isn't a "saved passwords" thing, I do not save passwords in the browser or in GoogleSync; I have a separate password manager for that, and that one isn't even capable of detecting the login modal that the Orbi UI uses instead of a login webpage anyway).

It's extremely odd and slightly troubling, but at least I'm confident that it's not a gaping hole; it's not like anyone from the outside, or even on my network, will be let through into the router UI; it seems that it's only a browser that is logged into my personal GoogleSync account is going to be able to get in; and that's at least as secure as (if not more than) the login for the UI.

EDIT TO ADD: My firmware is V4.6.8.2_2.1.9, in case that matters.