Unfortunately, I don't have an answer; only the same question posed by jjguitarist.
I believe when UC software updated in my Studio 192 all the mix scenes were lost.
This is not an acceptable situation as it deletes users work without advising them before hand or providing any options to avoid it.
If the Studio 192 implementation has a means for backing up mix scenes, or restoring them post-update, I haven't found it.
If this is how UC is intended to work then surely many others have been affected by this problem.