only in patch2:
unchanged:
--- a/core/modules/migrate_drupal_ui/src/Batch/MigrateUpgradeImportBatch.php
+++ b/core/modules/migrate_drupal_ui/src/Batch/MigrateUpgradeImportBatch.php
@@ -114,10 +114,10 @@ public static function run($initial_ids, $config, &$context) {
     // @todo Find a way to avoid this in https://www.drupal.org/node/2804611.
     if ($definition['destination']['plugin'] === 'entity:file') {
       // Make sure we have a single trailing slash.
-      if ($definition['source']['plugin'] === 'd7_file_private') {
+      $configuration['source']['constants']['source_base_path'] = rtrim($config['source_base_path'], '/') . '/';
+      if ($definition['source']['scheme'] === 'private') {
         $configuration['source']['constants']['source_base_path'] = rtrim($config['source_private_file_path'], '/') . '/';
       }
-      $configuration['source']['constants']['source_base_path'] = rtrim($config['source_base_path'], '/') . '/';
     }
 
     /** @var \Drupal\migrate\Plugin\Migration $migration */
only in patch2:
unchanged:
--- a/core/modules/migrate_drupal_ui/src/Form/ReviewForm.php
+++ b/core/modules/migrate_drupal_ui/src/Form/ReviewForm.php
@@ -228,6 +228,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
    */
   public function submitForm(array &$form, FormStateInterface $form_state) {
     $config['source_base_path'] = $this->store->get('source_base_path');
+    $config['source_private_file_path'] = $this->store->get('source_private_file_path');
     $batch = [
       'title' => $this->t('Running upgrade'),
       'progress_message' => '',