Steps:

1. Create landing page.
2. Add Form block.
3. Click Select content and go to Create tab.
4. Select language, Content Type and Location and click Create content.
5. Fill Title and click Create form - select Date field.
6. Click Publish.

Actual result:
Error occurs

 The "format" option should contain the letters "y", "M" or "d". Its current value is "". [in vendor/symfony/symfony/src/Symfony/Component/Form/Extension/Core/Type/DateType.php:60]

Expected result:
Error is not thrown, form is published.

Simplified steps:
1. Go to dashboard.
2. Click on Create button.
3. Start creating a form content.
4. Fill Title and click Create form - select Date field.
5. Click Publish.