Above the top ruler I should be able to see a tab, or multiple tabs when several files are open. However all that is shown is a cropped "Ai" ident. This means the only way I can flick between files is by through "Window" in the top panel.
Please accept my sincere apology for the inconvenience. Please get in touch with us at any of the other support channels – https://helpx.adobe.com/support.html . Since this is not a generic issue that we can reproduce at our end, we will need someone to look into your machine to figure out what is going on here.
This continues to be discussed in the forum. https://forums.adobe.com/message/10810107 There is still no solution. How long will this continue?