I found this bug when I went to the definition of the Flutter Navigator class. I'm running version 3.7.1 of the Dart and Flutter VSCode extensions.

Steps to reproduce the bug:

1. Click on NavigatorState in my code (the Flutter class probably doesn't matter but this is how I found the bug).
2. The file navigator.dart opens in VSCode. Clicking on the Flutter icon in the sidebar correctly shows an outline for the Flutter / Dart code.
3. Click on a tab of a different file in the editor. In my case, it was one of my project files. An outline of the Flutter / Dart code is properly displayed.
4. Click back on the navigator.dart tab in the editor. The Flutter outline pane is blank.

If I close and reopen the navigator.dart file the Flutter outline is displayed but whenever I click to view another file then click back the navigator.dart Flutter outline is blank.