The block and media folder trees don't show up in the assets pane.
- Go to admin view -> Config tab -> Manage Websites -> Websites tab.
- Click the affected site.
- Uncheck the Use site-specific assets box and click Save.
- Go back to edit view. Make sure you can see the blocks and media folder trees in the assets pane.
- Go back to admin view. Check the Use site-specific assets checkbox again and click Save.