Edit that content and press Ctrl+Shift+F immediately.
The search side bar opens (and works fine), but the recently made edits to the note are gone. I guess it loads some previously saved state.
Presumably the plugin should first trigger a save from the user-visible text box to Joplins internal storage before replacing the UI with the two-pane layout that allows displaying the side bar.
I don't think there's anything I can do about that. All the plugin is doing is toggling the visibility of its webview panel. I don't have any control over what Joplin does beyond that:
Reproduction:
Presumably the plugin should first trigger a save from the user-visible text box to Joplins internal storage before replacing the UI with the two-pane layout that allows displaying the side bar.