Problem
When editing in Camtasia Editor or rendering in Camtasia Editor, your computer will automatically restart or shutdown.
Solution
If you are running Time Machine backup while using Camtasia Editor, please turn it off completely and see if that corrects your issue while you use Camtasia Editor.
If you are running any other automatic software backup while Camtasia Editor is in use, please turn that off as well and attempt to use Camtasia Editor.