After updating to the latest version 2.1.3674 I was met with "A fatal error occurred for unknown reasons." on the sign-in screen. After signing in I found that all of my settings and profiles were gone. I have my worlds saved in a different directory for accessibility so worlds were unaffected, and I also noted that the versions folder still contained all clients that I previously had. However, all of my launcher settings were overwritten with the default settings, so I will have to manually write all of my profile settings again.