Summary: This occurred with a customer upgrading from 11.4 to 11.8 and when on 11.8 they selected the "Key Display & Mashup's screen", and tried to edit by adding more to the mashup, the 'edit button' was not visible, it disappeared.
As you can see there's no 'edit' button
Confirmed that the Role Based Security was set to Administrator
Solution: If you do see this issue and cannot see that "Edit" button, restarting IIS resolved this issue. I had the customer try other users, other browsers and even restarting the Windows Server and that did not resolve.
To restart IIS: 1 of 2 ways
- open up "Services" >find World Wide Web Publishing Service>Select 'Stop'/'Start' (do not just 'restart')
2. Or you can open IIS Manager and navigate per the screenshot steps below
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