I don't know anything about the Nokia Xpress browser, but given that it's the only browser giving that error, I'm inclined to think that it's an issue particular to that browser. You might contact their support to find out why they might be reporting a 406 Not acceptable error when one is not being returned by the server. That's definitely odd and inexplicable behavior.
For what it's worth, I don't think that the domain name (*.infopop.cc) has anything to do with this issue. You can see from the example I linked that the domain name is different (which I'm guessing would give you the same issue).
We have investigated this fairly extensively previously, and unfortunately, Microsoft is not at all transparent in this magical behavior that they are performing. They don't give any indication why their browser gives a "Search for app in the Store?" error message. If you search online for that issue, you'll see many other web developers confused about how/when/why Microsoft chooses to give that message. Without knowing why, it's hard for developers and operations teams to "fix" or change the behavior.
As you know, the Eve community platform has been successfully serving pages to all popular web browsers without issue for well over a decade. Given that nothing has changed in this regard with our web service and that it works in every other modern browser, it seems to me that the responsibility for this issue lies primarily with the Windows Phone browser software. We would fix any issues that are within our control, but we've been unable to identify any as of yet.
Is Microsoft support able to provide more concrete suggestions as to what the issue might be? Their generic "double check that the mime types were all supported at the server end" response is unfortunately not very helpful to us