Fatal error: Uncaught TypeError: call_user_func_array(): Argument #1 ($callback) must be a valid callback, function "wp_load_classic_theme_block_styles_on_demand" not found or invalid function name in /usr/www/users/izaksejqqd/wp-includes/class-wp-hook.php:324
Stack trace:
#0 /usr/www/users/izaksejqqd/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters(NULL, Array)
#1 /usr/www/users/izaksejqqd/wp-includes/plugin.php(522): WP_Hook->do_action(Array)
#2 /usr/www/users/izaksejqqd/wp-settings.php(727): do_action('init')
#3 /usr/www/users/izaksejqqd/wp-config.php(93): require_once('/usr/www/users/...')
#4 /usr/www/users/izaksejqqd/wp-load.php(50): require_once('/usr/www/users/...')
#5 /usr/www/users/izaksejqqd/wp-blog-header.php(13): require_once('/usr/www/users/...')
#6 /usr/www/users/izaksejqqd/index.php(17): require('/usr/www/users/...')
#7 {main}
  thrown in /usr/www/users/izaksejqqd/wp-includes/class-wp-hook.php on line 324