In case this means anything:

jlig, I think you will find that this is not a CF2016 issue, by which I mean if you think CF2016 is causing the prompt, it seems it is not. That login screen seems clearly some custom code, not CF-generated.
Let me propose something that may help both prove this and perhaps identify where the problem lies.
In that directory, where the you are calling that crmlogin.cfm, create a new folder called test. In that folder, create a blank test.cfm page and a blank application.cfm. Then call that as yourip/CRM/test/test.cfm. Do you get the prompt? If not, then clearly that prompt you saw was coming from SOME code. (Why? Because the blank application.cfm file stops CF from finding an application.cf* file in the CRM or higher folders, which means this test.cfm is now NOT executing that other application.cfm.)
Now, I appreciate that you may think that the login is NOT coming from any code of yours.
First, just consider the possibility that it MAY be there, and it may be that it appears because you’ve got code in there which has conditional logic that perhaps works one way if the domain name used is that for your site (as you may use on a server where things "work"), but it may work another way when you’ve used the IP address like you have, to run the site. (I’ve seen code like that cause confusion like this for years.)
Or back to the test.cfm example above, if that does NOT get the prompt, then again it’s got to be coming from SOME application.cfm or application.cfc, either in the CRM folder, or in its parent, or in its parent, all the way to the root of the drive where this code lives. (And catch that last point: it COULD be possible that you have no application.cf* file in the CRM folder, or the root folder for the site, and perhaps it’s ending up finding one ABOVE THAT, that perhaps you did not create. And CF10 added an ability in the CF Admin to tell that search to STOP at the webroot, if that interested you or anyone reading this.)
Let us know what the test shows.
/charlie