All our current Users are unable to add any entries to Trusted Sites in IE.
Very similar to https://social.technet.microsoft.com/Forums/windows/en-US/04a84c3e-0b02-4ca3-886d-126e5682b113/can-not-add-entries-to-trusted-sites-list?forum=winserverGP we are able to go into Trusted Sites and type the URL and click Add to see the item displayed, but after clicking Ok then going back into 'Sites' the item is no longer there.
If I check the registry the items are listed, but nothing in UI of Internet Explorer, and the site is not processed by IE.
We have tested to the point we know it is only a User setting somewhere in their profile/registry but not sure how to proceed. We can override using Computer Settings (Zone / Assignment) but we do not want to do this as it locks the User out.