I have restarted Unity to double check if the bug was a crash or something. It appears to persist so I think it may be a bug.
AC v1.7a in use
The "Add new action" button disappears from existing cut-scene objects. Also actions which exist are 'lost' and can't be recovered.
My solution has been to delete the cut-scene object and make it from scratch again.
I wonder if it's a reboot computer 'solve' and nobody else can replicate this bug?
Comments
From then it never happened and i hope Will never happen!
I dont know if was a unity bug or a ac bug...