diff -u b/core/modules/migrate_drupal_ui/src/Batch/MigrateUpgradeImportBatch.php b/core/modules/migrate_drupal_ui/src/Batch/MigrateUpgradeImportBatch.php
--- b/core/modules/migrate_drupal_ui/src/Batch/MigrateUpgradeImportBatch.php
+++ b/core/modules/migrate_drupal_ui/src/Batch/MigrateUpgradeImportBatch.php
@@ -30,7 +30,7 @@
    *
    * @var int
    */
-  static $numProcessed = 0;
+  protected static $numProcessed = 0;
 
   /**
    * Ensure we only add the listeners once per request.
@@ -56,7 +56,7 @@
   protected static $messages;
 
   /**
-   * Runs a single migrate import batch.
+   * Runs a single migrate batch import.
    *
    * @param int[] $initial_ids
    *   The full set of migration IDs to import.
@@ -64,7 +64,6 @@
    *   An array of additional configuration from the form.
    * @param array $context
    *   The batch context.
-   *
    */
   public static function run($initial_ids, $config, &$context) {
     if (!static::$listenersAdded) {