Being asked to sign in to web map where all features are shared publicly and anonymous access is enabled at org level.

[MDB_GIS]

Here is a link to the map: <Redacted>

The link will take you to the overview page, which loads without issue. But then when you open the map, the map appears to briefly try and load before a login screen pops up. I have tried going through the developer console but I don't see anything indicating what is responsible for the login screen. 

[Ed_]

It's opening fine for me didn't get sign-in popup 

but i would advice you to migrate your "public data map" to a basic map Instant App and make that public. Security wise it's not a good idea to share your web map like this.

[MDB_GIS · Accepted solution]

Thankfully I was able to resolve the issue. The problem was a result of AGO assistant doing an incomplete job of 'replacing service URLs.' For some reason despite clearly reflecting in the AGO UI that the service URL was correct, it had only actually updated one of the 7 copies  of the water meter layer. All of the other references were still to the original layer, which had security enabled. I copied the JSON out to a text editor, found and replaced all of the incorrect references, and then updated the JSON in AGO Assistant. That fixed the issue! 

Regarding the instant app, yes, that is the plan! This was just a quick and dirty map trying to diagnose the problem before proceeding any further.