User Meta Prefix issue and WP 5.1 Compatibility

This plugin is great, but I recently found 2 issues with it:

1. WP 5.1 depreciated the wpmu_create_blog action so the plugin should get updated. I modified my copy to use the new wp_initialize_site action easily.
2. The code to copy the user meta looks only for the DB prefix _ blog_id – it doesn’t check for the trailing _ after blog_id, so if you have a default blog with ID = 2, it starts matching against blog_id = 20, 21, 22 etc leading to enormous duplication of data. I ended up with 27,000 records in my usermeta table very quickly (when it was only supposed to be duplicating 5 records). This leads to huge problems quickly. Here’s the code I used to fix the issue:

// Copy users
if ( $copy_users ){
		$users = get_users('blog_id='.$id_default_blog);
		$default_prefix = $prefix . $id_default_blog . '_';
		$default_prefix_len = strlen($default_prefix);
		$new_prefix = $wpdb->get_blog_prefix();

		function user_array_map( $a ){ return $a[0]; }

		foreach($users as $user){
				$all_meta = array_map( 'user_array_map', get_user_meta( $user->ID ) );
				foreach ($all_meta as $metakey => $metavalue) {
						if(substr($metakey, 0, $default_prefix_len) == $default_prefix) {
								$raw_meta_name = substr($metakey,$default_prefix_len);
								update_user_meta( $user->ID, $new_prefix . $raw_meta_name, maybe_unserialize($metavalue) );
						}
				}
		} 
}