I have recently updated to v1.9.1 and now unable to launch the app. I see it trying to load, but then it never actually launches and it then disappears from top bar.
Try to start it from the terminal via mailspring and see, if you get an error message there. You can try to uninstall Mailspring, delete your configuration directory ~/.config/Mailspring (this will delete your mail config and all emails stored on your system) and reinstall the app. If you are lucky, this may help.