In IE11, why some machines requires the website URL included in "Compatibility view settings" and others doesn't?

Question

I have a website that requires to run in compatibility mode.

We use

<meta http-equiv="X-UA-Compatible" content="IE=EmulateIE9">

to force this behavior and it works fine in IE 9, IE 10, and it works fine in some machines with IE 11 without changes, but in other machines with the same version of IE11, same windows version it requires to add the website URL to the "Compatibility view settings". Once added everything works fine.

Using developer tools (F12)

When you use the developer tools to change the Document mode, some machines will display the full list of options (Edge, 10, 9, 8, 7, 5) in other machines you must add the URL to the "Compatibility view settings" to view the full list of options, otherwise only Edge is available.

Why IE11 behaves different in two different machines having the same exact settings?

Is there any windows settings that could be causing different behavior?

Is there anything I can do in the web page code to force IE to behave the same?

Answer 1

It could be that Internet Explorer is affected by Enterprise Mode on those pages. Do you see a blue icon with a white building in it to the left of the URL?

Microsoft have this article 'Fix web compatibility issues using document modes and the Enterprise Mode site list' explaining the different document modes and how Enterprise Mode affects these views.

These are the Registry keys to investigate to know if Enterprise Mode is enabled on the affected machine:

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Internet Explorer\Main\EnterpriseMode
HKEY_CURRENT_USER\SOFTWARE\Policies\Microsoft\Internet Explorer\Main\EnterpriseMode