diff -u b/core/lib/Drupal/Core/Config/ConfigImporter.php b/core/lib/Drupal/Core/Config/ConfigImporter.php
--- b/core/lib/Drupal/Core/Config/ConfigImporter.php
+++ b/core/lib/Drupal/Core/Config/ConfigImporter.php
@@ -727,9 +727,10 @@
         }
       }
       $this->eventDispatcher->dispatch(ConfigEvents::IMPORT_VALIDATE, new ConfigImporterEvent($this));
-      if (count($this->getErrors())) {
-        $errors = array_merge('There were errors validating the config synchronization.', $this->getErrors());
-        throw new ConfigImporterException(SafeMarkup::checkPlain(implode("\n", $errors)));
+      $errors = $errors = $this->getErrors();
+      if (count($errors)) {
+        array_unshift($errors, 'There were errors validating the config synchronization:');
+        throw new ConfigImporterException(SafeMarkup::checkPlain(implode(" ", $errors)));
       }
       else {
         $this->validated = TRUE;
@@ -756,7 +757,7 @@
   protected function processConfiguration($collection, $op, $name) {
     try {
       $processed = FALSE;
-      if ($this->configManager->supportsConfigurationEntities($collection)) {
+      if ($collection == StorageInterface::DEFAULT_COLLECTION) {
         $processed = $this->importInvokeOwner($collection, $op, $name);
       }
       if (!$processed) {