SourceTree freezes during startup in OS 10.11 (El Capitan)

Note: This affects 2.0.5.3 as well. (It is not yet available in the "Affects Version/s" dropdown list)

For some users, when they open up SourceTree in El Capitan, it freezes (but does not crash).

If user performs a right click on the SourceTree app at the dock, user will find that there's another window called "Authenticate" behind the scene, but no one will be able to reach to that window:

The only known workaround is to wipe off SourceTree's preferences, and then perform a backup:

• https://confluence.atlassian.com/display/SOURCETREEKB/Wiping+SourceTree+Preferences

SourceTree will then run smoothly.