Step 1: Open System Preferences
Step 2: Click Security & Privacy
Step 3: Click the Privacy Tab
Step 4: Click the Accessibility section
Step 5: Click the Lock button in the bottom left-hand corner and enter your password
Step 6: Check the box next to Snagit under the “Allow the apps below to control your computer.”
Step 7: Quit Snagit, and relaunch — scrolling capture should now work as intended.
If you have any other problems with it don't hesitate to let us know.