Apple made lots of security updates with Mojave OS. All the apps are now under strict control of what they can and can not access on your computer.
Defaulter uses Pro Tools to send commands to OS, and then it uses OS to send commands to Pro Tools.
For this to keep working in Mojave and above, you have to allow Pro Tools to control your computer in the System Preferences.
Go to Sytem Preferences-> Security & Privacy -> Select Privacy tab and then the Accessibility tab on the left column. Click the box next to Pro Tools to allow access.
