I switched debug mode on. I've cured the problem. Here's what was being reported in debug mode:
Fatal error: Uncaught Error: Undefined class constant 'CALLBACK_GET_VIEW_BLOCK_PREVIEW' in /home/xxx/public_html/wp-ttvr/wp-content/plugins/wp-views/application/controllers/compatibility/editor-blocks/blocks/view/view.php:61 Stack trace: #0 /home/xxx/public_html/wp-ttvr/wp-includes/class-wp-hook.php(286): OTGSToolsetViewsControllerCompatibilityEditorBlocksViewBlock->register_block_editor_assets('') #1 /home/xxx/public_html/wp-ttvr/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters(NULL, Array) #2 /home/xxx/public_html/wp-ttvr/wp-includes/plugin.php(453): WP_Hook->do_action(Array) #3 /home/xxx/public_html/wp-ttvr/wp-settings.php(450): do_action('init') #4 /home/xxx/public_html/wp-ttvr/wp-config.php(89): require_once('/home/xxx...') #5 /home/xxx/public_html/wp-ttvr/wp-load.php(37): require_once('/home/xxx...') #6 /home/xxx/public_html/wp-ttvr/wp-blog-header.php(13): require_once('/home/xxx...') #7 /home/xxx in /home/xxx/public_html/wp-ttvr/wp-content/plugins/wp-views/application/controllers/compatibility/editor-blocks/blocks/view/view.php on line 61
Please try the following troubleshooting steps:
1. If you have not already rolled back to a previous version, log in to the server via FTP and go to wp-content/plugins/. Rename the folder wp-views to be wp-views-backup.
2. Go to wp-admin > Plugins > Installed Plugins. You will see a message that Views has been deactivated. Now deactivate all other Toolset plugins temporarily.
3. Delete the Views plugin and reinstall the latest version. You can download the Views plugin from https://toolset.com/account/downloads
4. If Types is not up-to-date, be sure to update Types. Then activate Types and Views. Check to see if any errors appear.
5. Update all other Toolset plugins to the latest versions, then activate them one by one until the problem returns or all the desired plugins are active.
