Warning: Array to string conversion in pluggable.php

Hi,

This erroe appeared on the top of my site.

Warning: Array to string conversion in /home/klimatis/public_html/wp-includes/pluggable.php on line 2279

I have checked line 2279: $nonce = (string) $nonce;

Full code:

if ( ! function_exists( 'wp_verify_nonce' ) ) :
	/**
	 * Verifies that a correct security nonce was used with time limit.
	 *
	 * A nonce is valid for 24 hours (by default).
	 *
	 * @since 2.0.3
	 *
	 * @param string     $nonce  Nonce value that was used for verification, usually via a form field.
	 * @param string|int $action Should give context to what is taking place and be the same when nonce was created.
	 * @return int|false 1 if the nonce is valid and generated between 0-12 hours ago,
	 *                   2 if the nonce is valid and generated between 12-24 hours ago.
	 *                   False if the nonce is invalid.
	 */
	function wp_verify_nonce( $nonce, $action = -1 ) {
		$nonce = (string) $nonce;
		$user  = wp_get_current_user();
		$uid   = (int) $user->ID;
		if ( ! $uid ) {
			/**
			 * Filters whether the user who generated the nonce is logged out.
			 *
			 * @since 3.5.0
			 *
			 * @param int        $uid    ID of the nonce-owning user.
			 * @param string|int $action The nonce action, or -1 if none was provided.
			 */
			$uid = apply_filters( 'nonce_user_logged_out', $uid, $action );
		}

		if ( empty( $nonce ) ) {
			return false;
		}

		$token = wp_get_session_token();
		$i     = wp_nonce_tick( $action );

		// Nonce generated 0-12 hours ago.
		$expected = substr( wp_hash( $i . '|' . $action . '|' . $uid . '|' . $token, 'nonce' ), -12, 10 );
		if ( hash_equals( $expected, $nonce ) ) {
			return 1;
		}

		// Nonce generated 12-24 hours ago.
		$expected = substr( wp_hash( ( $i - 1 ) . '|' . $action . '|' . $uid . '|' . $token, 'nonce' ), -12, 10 );
		if ( hash_equals( $expected, $nonce ) ) {
			return 2;
		}

		/**
		 * Fires when nonce verification fails.
		 *
		 * @since 4.4.0
		 *
		 * @param string     $nonce  The invalid nonce.
		 * @param string|int $action The nonce action.
		 * @param WP_User    $user   The current user object.
		 * @param string     $token  The user's session token.
		 */
		do_action( 'wp_verify_nonce_failed', $nonce, $action, $user, $token );

		// Invalid nonce.
		return false;
	}
endif;