A solution if you need to separate some custom fields data from the table wp_usermeta for any reason.

customtable-wp-usermeta.php

<?php

/*
* Custom WP Usermeta Table
*
* Version: 1.0
* Author: Edir Pedro
* Website: https://gist.github.com/edirpedro/528c671b31557be8769620337e2b44a0
*
* How to use?
*
* 1) Duplicate the original "wp_usermeta" table and set a suffix like "wp_usermeta_tablename".
* 2) Add the new table: CustomUsermetaTable::add("tablename", "fieldprefix");
* 3) Remember to use ALL your custom fields name like "fieldprefix_fieldname" 
*    to automatically redirect the data to your new table.
*
*/

class CustomUsermetaTable {
	
	static private $tables = array();
	
	// Add new table setting the table suffix and the field prefix
	static public function add($name, $prefix) {
		global $wpdb;
		
		// Adding new table
		self::$tables[] = array(
			'name' => $wpdb->usermeta . '_' . $name,
			'prefix' => $prefix . '_'
			);

		// Hooks
		add_filter('add_user_metadata', array(__CLASS__, 'update_metadata'), 0, 4);
		add_filter('update_user_metadata', array(__CLASS__, 'update_metadata'), 0, 4);
		add_filter('get_user_metadata', array(__CLASS__, 'get_metadata'), 0, 3);
		add_filter('delete_user_metadata', array(__CLASS__, 'delete_metadata'), 0, 3 );
	
	}
	
	// Return a table if the prefix exists in custom data
	static private function get_table($meta_key) {
		foreach(self::$tables as $key => $table) {
			$prefix = $table['prefix'];
			if(strpos($meta_key, $prefix) === 0 || strpos($meta_key, "_$prefix") === 0) // Checking WP and ACF extra field
				return self::$tables[$key];
		}
		return false;
	}

	// Update or Add the custom data
	static public function update_metadata($check, $user_id, $meta_key, $meta_value) {
		global $wpdb;
		
		$table = self::get_table($meta_key);
		if(!empty($table)) {
			$table = $table['name'];
			$data = array(
				'user_id' => $user_id,
				'meta_key' => $meta_key,
				'meta_value' => maybe_serialize($meta_value)
				);
			$query = $wpdb->prepare("SELECT umeta_id FROM $table WHERE meta_key = %s AND user_id = %d", $meta_key, $user_id);
			$id = $wpdb->get_var($query);		
			if(empty($id))
				return $wpdb->insert($table, $data);
			else
				return $wpdb->update($table, $data, array('umeta_id' => $id));
		}
	
		return $check;
	}
	
	// Get custom data
	static public function get_metadata($check, $user_id, $meta_key) {
		global $wpdb;
		
		$table = self::get_table($meta_key);
		if(!empty($table)) {
			$table = $table['name'];
			$query = $wpdb->prepare("SELECT meta_value FROM $table WHERE meta_key = %s AND user_id = %d", $meta_key, $user_id);
			return $wpdb->get_col($query);
		}
		
		return $check;
	}
	
	// Delete custom data
	static public function delete_metadata($check, $user_id, $meta_key) {
		global $wpdb;
		
		$table = self::get_table($meta_key);
		if(!empty($table)) {
			return $wpdb->delete($table['name'], array('meta_key' => $meta_key, 'user_id' => $user_id));
		}
		
		return $check;
	}
	
}
	
	
?>