We upgraded to SharePoint 2013 Online yesterday. Today a user has told me that when she clicks on the ribbon tabs for a list that the tabs disappear. I have not been able to confirm with her yet if this is happening on every list, or just the
one. It does not happen with me (administrator) or with my test user account (Member). The page has not been edited in any way as far as new web parts or masterpage editing (some common reasons I saw for this).
There are no mistakes; every result tells you something of value about what you are trying to accomplish.
