Edward has covered this in several posts on this forum including https://www.zero88.com/forum/topic/10062-ad-as-additional-adress-unpatch-missing/#comment-42186 , where RigSync had repatched a fixture so the "Add As Additional" button was not available. I have pasted these comments as they may be relevant :
Setup > Fixture Schedule > tap on a fixture's DMX address to open "Edit DMX Address". If the "DMX Universe", "Unpatch", and "Add As Additional" buttons are hidden, this indicates that the selected fixture is an RDM device that has been discovered by RigSync. It is not possible to unpatch a fixture discovered by RigSync, or give it multiple start addresses.
Sorry to hear that RigSync changed the settings of RDM fixtures when you didn't want it to. If you go to Setup > Universes > Remote Device Management, there is a "Revert Rig Back" button, which will tell the fixtures to go back to the settings they had when the console found them.
You would need to re-patch the fixture manually, to be able to access the "Add As Additional" and "Unpatch" buttons.
Obsidians gain is our loss unfortunately.