Constraint on paragraph field not working Here is a very simple code:
1-My constraint plugin (MyConstraint.php)
/**
 * @Constraint(
 *   id = &quot;MyConstraint&quot;,
 *   label = @Translation(&quot;Never Validated&quot;, context = &quot;Validation&quot;),
 *   type = &quot;string&quot;
 * )
 */
class MyConstraint extends Constraint {
  public $message = &quot;error %value&quot;;
}

2-My constraint validator (MyConstraintValidator.php) [=&gt;addViolation in all cases]
class MyConstraintValidator extends ConstraintValidator {

  public function validate($items, Constraint $constraint) {
    dpm(&quot;I am displayed&quot;);
    $this-&gt;context-&gt;addViolation($constraint-&gt;message, [
              '%value' =&gt; 10
            ]);
    return;
}

3-My constraint added to my bundle
function mymodule_entity_bundle_field_info_alter(&amp;$fields, EntityTypeInterface $entity_type, $bundle)
{
    if($bundle=='my_bundle'){
      $fields['my_paragraph_field']-&gt;addConstraint('MyConstraint', []);
    }
}

Result:
1-The dpm message 'I am displayed' is displayed
2-The entity is saved without any validation error
Notes:
-I have other constraints which are working well, If I test one of them (on my_bundle), the violation of this working constraint will be displayed but not the one with the code detailled here.
-The problematic constraint is added to a paragraph field... I suspect the problem is coming from there
-Nothing in the error logs.
I am looking for a hint to where to look.
On your addConstraint() your second parameter is an empty array - if you do not want to add any options leave that empty or use NULL