FAQ Group Error when in preview

Problem/Motivation

When previewing FAQ without saving first, I'm getting the following error:
The website encountered an unexpected error. Try again later.

AssertionError: Cannot load the "block_content" entity with NULL ID. in assert() (line 261 of core/lib/Drupal/Core/Entity/EntityStorageBase.php).

Steps to reproduce

Create or edit an FAQ page
Add a Group and Group item
Do not save, click Preview