Unable logging into 1 website, across all browsers, from win10 laptop

[DDDietmar]

For over a week now, I have been unable to log into a javascript-heavy website hosted on azurewebsites.net from my HP Envy laptop with any of my installed browsers (FF, IE, Edge, Chrome). I am able to log in from other devices (tried one acer laptop, my android phone, and the site admins also report that my account is in good standing).

I have all updates on my win10-64bit machine. I have done the following:

- tried wifi and lan connection (the router seems find as it allows connection with that acer laptop) as well as tethering through my phone

- ran a malwarebytes virus scan, including rootkits

- copied the internet options from the acer laptop

- cleared everything cached

- disabled windows defender firewall

- ran windows troubleshooters

I cannot revert to a restore point ("previous version of windows 10") because my computer "has been updated more than 10 days ago"). The "automatic repair" option in the recovery menu seems unavailable to me (is this a HP modification of windows?).

As I've mentioned, the site is heavy on javascript - there is no straight html in there. Going through the firefox inspector, I am noticing an error upon submit of the login form:

XHRPOST https://siteapi.azurewebsites.net/api/users/login
[HTTP/1.1 401 Unauthorized 175ms]

Object { headers: {…}, status: 401, statusText: "Unauthorized", url: "https://siteapi.azurewebsites.net/api/users/login", ok: false, name: "HttpErrorResponse", message: "Http failure response for https://siteapi.azurewebsites.net/api/users/login: 401 Unauthorized", error: null }

Note that the address in the addressbar is a different one:

https://site.azurewebsites.net/login

(note that I am not giving you the real address - "site" is standing in for it.)

Thank you for reviewing!

[DDDietmar]

I've since checked that I am allowing cross-domain content, also reset internet options first, just in case.