Site editor: transition of preview pane from/to home spoiled by remount

[stokesman]

Description

The transition when navigating to or from the home route to others that include the preview pane has degraded since 6.7. The animation is still there but there are some frames where the content vanishes. This is most notable navigating to or from the pages route but it’s possible to see going from the templates route when the list view is used.

Step-by-step reproduction instructions

1. Open the site editor
2. Go to "Pages" and note the content in the preview pane blanks out for a moment
3. Go back to the home view and note the content in the preview pane blanks out for a moment

Screenshots, screen recording, code snippet

site-editor-preview-remounts.mp4

Environment info

• WP 6.7.1 with Gutenberg plugin at trunk
• Chrome
• macOS

Please confirm that you have searched existing issues in the repo.

• Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

• Yes

Please confirm which theme type you used for testing.

• Block
• Classic
• Hybrid (e.g. classic with theme.json)
• Not sure