After changing permissions of (a lot of) files on git, SourceTree detected these unstaged changes and became unresponsive when trying to refresh. I quit it when the unresponsiveness was taking too long. After restarting the program again, it did not launch.
I checked the activity monitor and SourceTree is labeled 'application not responding'. Used Force quit and restarted the Mac. SourceTree is still not responding. How to run SourceTree again?
Ok I solved this one by deleting the folder Library/Application Support/SourceTree. After that I can now open the program again and scan my directory of projects for import.
The unresponsiveness was due to the changed file permissions of my project repo. Before I can open this said repo I accessed the project files' .git/config and set the config.fileMode to false.