Description

The pattern explorer is not listing any patterns in the site-editor. The pattern explorer works in the post editor, and it works in the sidebar view.

Step-by-step reproduction instructions

1. Go to Appearance → Editor
2. Click on the canvas on the right
3. Press the + icon at the top left of the screen
4. Press the patterns tab
5. Notice some pattern categories are listed and clicking on them previews a pattern
6. Go to the bottom of the category list and press "Explore all patterns"
7. Notice a huge dialog appears with categories to the left and a blank area to the right

Screenshots, screen recording, code snippet

Environment info

I'm using GB trunk (f3c0586) with TT4 as the active theme. It also repros in GB 17.9.0 but not I'm told, in GB 17.7.0

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