reverted:
--- b/core/lib/Drupal/Core/Field/FieldItemList.php
+++ a/core/lib/Drupal/Core/Field/FieldItemList.php
@@ -280,8 +280,7 @@
         ->getValidationConstraintManager()
         ->create('Count', [
           'max' => $cardinality,
+          'maxMessage' => t('%name: this field cannot hold more than @count values.', ['%name' => $this->getFieldDefinition()->getLabel(), '@count' => $cardinality]),
-          'maxMessage' => t('%name: 
-          this field cannot hold more than @count values.', ['%name' => $this->getFieldDefinition()->getLabel(), '@count' => $cardinality]),
         ]);
     }