We ran into a hiccup recently where several computers were not keeping a site in the Compatibility View list. You could add the site, but when you restarted Internet Explorer, it was gone. This was caused because the option Delete browsing history on exit was enabled. This is a known issue and has been known since IE 8. This client is using IE 11.
|Internet Explorer - Internet Options|
- Policies\Administrative Templates\Windows Components\Internet Explorer\Compatibility View\Use Policy List of Internet Explorer 7 sites
|GP Setting for List of Compatibility View Sites|
To use the Developer Tools option in IE, press F12. This opens a pane at the bottom of the IE window. Select the Emulation tab and read the value listed for Document mode. If this value is 7 (Default) then it is using Compatibility View.
|IE 11 - Developer Tools|