Repro is with Zui v1.0.0 on Ubuntu Linux. This issue was originally reported by a community user in a public Slack message.

As shown in the attached video, if the contents of the "Details" view are popped out into their own separate window, and then the app's main window gets closed somehow, when the app is ultimately quit and relaunched, it comes back with just the blank Detail window and no main window. I don't see a way to force it to re-open a main window when it's in this state.