Chromium based browser update blocks website when using CF DNS proxy setting

What is the name of the domain?

https://goamltst.fiaumalta.org/tst

What is the error number?

No error just the login popup doesnt show when you need to enter the fallback authentication code.

What is the error message?

No error just the login popup doesnt show when you need to enter the fallback authentication code.

What is the issue you’re encountering

The Fallback authentication popup in our website is not loading

What steps have you taken to resolve the issue?

If we disable the proxy it will work. It also works when directly running our website directly from the server.

What feature, service or problem is this related to?

DNS records

What are the steps to reproduce the issue?

When using Chrome or Edge, you need to login using a correct username and password and use the fallback 2FA to get the code with a different method and a popup should load to allow you to end the 2FA code, however the popup never loads.

Screenshot of the error

Resolved by removing a UI related custom header from our web.config file.

Custom header option to be removed/edited is the X-UA-Compatible" value=“IE=EmulateIE9”.