This has been fixed in the latest version of Snagit on Mac. To download the update, open Snagit and browse to the menu bar item Snagit > Check for updates. If you are still experiencing this problem after updating, please submit a support ticket.
When Snagit opens, the UI looks distorted (zoom controls and dimensions), and the capture is blank.
This is a known issue that our Engineers are currently investigating. This behavior can occur when attempting to open a .snagproj file while the Editor is closed. To resolve the issue, close out of Snagit and re-launch the Editor.