WP’s Legacy Widget aka ‘core/legacy-widget’ is missing on child multisite.

WP Version 5.8.1
PublishPress Version 2.10.5

Steps to Reproduce:
1. Use pre-existing WP Multisite.
2. Ensure PublishPress Blocks is active in plugins list.
3. Go to a child site; NOT the main site.
4. Go to Widgets, or Customizer > Widgets.
5. Click add widget, and search for ‘Legacy Widget’.
Result: Legacy Widget is missing.

Issue resolves when visiting Admin-Menu > Blocks.

I may be wrong, but it seems there may have been a change to settings data structure, and isn’t properly updating until settings are saved. Meanwhile, those that are having the issue may have struggle hunting down the culprit, and for those with many child sites would have to visit each site’s settings to clear the issue.

Also, an error was produced on the Widgets page with just PublishPress Blocks active. It may be unrelated, but thought I’d add it anyways.

[20-Sep-2021 09:30:42 UTC] PHP Notice:  wp_enqueue_script() was called <strong>incorrectly</strong>. "wp-editor" script should not be enqueued together with the new widgets editor (wp-edit-widgets or wp-customize-widgets). Please see <a href="https://www.ads-software.com/support/article/debugging-in-wordpress/">Debugging in WordPress</a> for more information. (This message was added in version 5.8.0.) in C:\Web-Projects\WP-src\WordPress-Multisite\wp-includes\functions.php on line 5663
[20-Sep-2021 09:30:42 UTC] PHP Stack trace:
[20-Sep-2021 09:30:42 UTC] PHP   1. {main}() C:\Web-Projects\WP-src\WordPress-Multisite\wp-admin\widgets.php:0
[20-Sep-2021 09:30:42 UTC] PHP   2. require() C:\Web-Projects\WP-src\WordPress-Multisite\wp-admin\widgets.php:31
[20-Sep-2021 09:30:42 UTC] PHP   3. require_once() C:\Web-Projects\WP-src\WordPress-Multisite\wp-admin\widgets-form-blocks.php:69
[20-Sep-2021 09:30:42 UTC] PHP   4. do_action() C:\Web-Projects\WP-src\WordPress-Multisite\wp-admin\admin-header.php:147
[20-Sep-2021 09:30:42 UTC] PHP   5. WP_Hook->do_action() C:\Web-Projects\WP-src\WordPress-Multisite\wp-includes\plugin.php:470
[20-Sep-2021 09:30:42 UTC] PHP   6. WP_Hook->apply_filters() C:\Web-Projects\WP-src\WordPress-Multisite\wp-includes\class-wp-hook.php:327
[20-Sep-2021 09:30:42 UTC] PHP   7. wp_check_widget_editor_deps() C:\Web-Projects\WP-src\WordPress-Multisite\wp-includes\class-wp-hook.php:303
[20-Sep-2021 09:30:42 UTC] PHP   8. _doing_it_wrong() C:\Web-Projects\WP-src\WordPress-Multisite\wp-includes\widgets.php:2039
[20-Sep-2021 09:30:42 UTC] PHP   9. trigger_error() C:\Web-Projects\WP-src\WordPress-Multisite\wp-includes\functions.php:5663