I had some problems with authorisation on a fairly new install of SourceTree, and decided to do an uninstall, cleanup, and reinstall to try to get back on track.
I followed instructions elsewhere to uninstall, remove Atlassian and Sourcetree folders in my C:\Users\<myuser>\Appdata\Local folder, and reboot and reinstallation. In addition, I removed all bitbucket related credentials in Windows Credential Manager.
Any attempt to start Sourcetree shows the app for a second or two and then disappears. Windows Event Log shows two errors a little similar to this ticket: https://confluence.atlassian.com/sourcetreekb/sourcetree-crashes-on-startup-831655339.html I tried solutions proposed there (though the user config file was not corrupted) and this did not work.
Having scanned the AppData\Local folder, I found this log entry in the SourceTree.log file:
ERROR [2020-06-23 07:51:21,458] [20] [SourceTree.Exceptions.RemoteHostException] [Log] - Insufficient authentication credentials
ERROR [2020-06-23 07:51:21,478] [1] [SourceTree.Exceptions.RemoteHostException] [Log] - Failed to list teams for user [XXXXXXXX_nij]
'XXXXXXXX_nij' is one of my bitcucket user names... BUT how does this installation know to search for that after all configuration folders have been cleaned up?