I have just fixed the issue and thought I would post what I did.
As the title says, Sonar would launch, I look in Activity Monitor and its there… and then disappears.
I downloaded a fresh copy, and replaced the app.
Next up, I grab the back up, in the Finder “Command Shift G” for and I go to
~/.config
in here you find a folder called NzbDrone, drag the whole folder out to you desktop.
Now launch Sonarr and see it this has solved the issue, Sonarr will recreate the NzbDrone folder for you.
If everything is great, go to Activity Monitor and kill Sonarr.
Now go to the NzbDrone folder on your desktop and go to Backups, extract the most recent and copy it back in. Relaunch Sonarr.
Robert’s your fathers brother.