diff --git a/wp-admin/includes/ajax-actions.php b/wp-admin/includes/ajax-actions.php
index b821c0e04c..4a30934a5e 100644
--- a/wp-admin/includes/ajax-actions.php
+++ b/wp-admin/includes/ajax-actions.php
@@ -4462,18 +4462,18 @@ function wp_ajax_update_plugin() {
 		$status['errorMessage'] = $skin->get_error_messages();
 		wp_send_json_error( $status );
 	} elseif ( is_array( $result ) && ! empty( $result[ $plugin ] ) ) {
-		$plugin_update_data = current( $result );
 
 		/*
-		 * If the `update_plugins` site transient is empty (e.g. when you update
-		 * two plugins in quick succession before the transient repopulates),
-		 * this may be the return.
+		 * Plugin is already at the latest version.
+		 *
+		 * This may also be the return value If the `update_plugins` site transient is empty,
+		 * e.g. when you update two plugins in quick succession before the transient repopulates.
 		 *
 		 * Preferably something can be done to ensure `update_plugins` isn't empty.
 		 * For now, surface some sort of error here.
 		 */
-		if ( true === $plugin_update_data ) {
-			$status['errorMessage'] = __( 'Plugin update failed.' );
+		if ( true === $result[ $plugin ] ) {
+			$status['errorMessage'] = $upgrader->strings['up_to_date'];
 			wp_send_json_error( $status );
 		}
 
@@ -4484,6 +4484,7 @@ function wp_ajax_update_plugin() {
 			/* translators: %s: Plugin version. */
 			$status['newVersion'] = sprintf( __( 'Version %s' ), $plugin_data['Version'] );
 		}
+
 		wp_send_json_success( $status );
 	} elseif ( false === $result ) {
 		global $wp_filesystem;
diff --git a/wp-admin/includes/class-plugin-upgrader.php b/wp-admin/includes/class-plugin-upgrader.php
index cad0a613ac..22f8221e7b 100644
--- a/wp-admin/includes/class-plugin-upgrader.php
+++ b/wp-admin/includes/class-plugin-upgrader.php
@@ -391,8 +391,8 @@ class Plugin_Upgrader extends WP_Upgrader {
 
 			unset( $past_failure_emails[ $plugin ] );
 		}
+
 		update_option( 'auto_plugin_theme_update_emails', $past_failure_emails );
-		reset( $results );
 
 		return $results;
 	}
diff --git a/wp-admin/includes/class-theme-upgrader.php b/wp-admin/includes/class-theme-upgrader.php
index 9dfb751d12..b5364c84ce 100644
--- a/wp-admin/includes/class-theme-upgrader.php
+++ b/wp-admin/includes/class-theme-upgrader.php
@@ -500,8 +500,8 @@ class Theme_Upgrader extends WP_Upgrader {
 
 			unset( $past_failure_emails[ $theme ] );
 		}
+
 		update_option( 'auto_plugin_theme_update_emails', $past_failure_emails );
-		reset( $results );
 
 		return $results;
 	}
diff --git a/wp-admin/includes/class-wp-upgrader.php b/wp-admin/includes/class-wp-upgrader.php
index d4244fb026..8b1cc4b5fb 100644
--- a/wp-admin/includes/class-wp-upgrader.php
+++ b/wp-admin/includes/class-wp-upgrader.php
@@ -660,7 +660,7 @@ class WP_Upgrader {
 	 *     @type array  $hook_extra                  Extra arguments to pass to the filter hooks called by
 	 *                                               WP_Upgrader::run().
 	 * }
-	 * @return array|false|WP_error The result from self::install_package() on success, otherwise a WP_Error,
+	 * @return array|false|WP_Error The result from self::install_package() on success, otherwise a WP_Error,
 	 *                              or false if unable to connect to the filesystem.
 	 */
 	public function run( $options ) {
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 679983422c..265320de08 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.5-beta1-48444';
+$wp_version = '5.5-beta1-48445';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.