"Customize User Logon Page" link on the 'Logon Settings' has disappeared after upgrade to 5815

"Customize User Logon Page" link on the 'Logon Settings' has disappeared after upgrade to 5815

I am unable now to see the "Customize User Logon Page" link on the Admin page.
We were running 5708, i upgraded to 5800 then 5815. At this point the Customize User Logon Page disappeared.

Is it somewhere else, or did I miss something in the upgrade?
How can I recover this, as i need to amend the User logon page.

Thanks

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