PHP notice "Undefined index: region" on layout overrides when using the Field Layout module

Layout Builder emits an "undefined index" PHP notice when overriding a bundle layout for an individual entity.

Steps to reproduce:

1. Enable both Layout builder and Field layout modules.
2. Go to the "Manage display" page of a particular bundle.
3. Go to the "Full content" view mode secondary tab and check both "Use Layout Builder" and "Allow each content item to have its layout customized."
4. On a particular entity, go to to the "Layout" tab.
5. See the PHP notice.

Original report:

I have and PHP Notice every time I open node (not bundle) layout settings.

Notice: Undefined index: region in Drupal\field_layout\FieldLayoutBuilder->buildForm() (line 109 of core/modules/field_layout/src/FieldLayoutBuilder.php).

And stackstrace:

Drupal\field_layout\FieldLayoutBuilder->buildForm(Array, Object) (Line: 64)
field_layout_form_alter(Array, Object, 'node_page_layout_builder_form') (Line: 539)
Drupal\Core\Extension\ModuleHandler->alter('form', Array, Object, 'node_page_layout_builder_form') (Line: 835)
Drupal\Core\Form\FormBuilder->prepareForm('node_page_layout_builder_form', Array, Object) (Line: 29)
Drupal\webprofiler\Form\FormBuilderWrapper->prepareForm('node_page_layout_builder_form', Array, Object) (Line: 277)
Drupal\Core\Form\FormBuilder->buildForm('node_page_layout_builder_form', Object) (Line: 93)
Drupal\Core\Controller\FormController->getContentResult(Object, Object)
call_user_func_array(Array, Array) (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 582)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 124)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) (Line: 97)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 151)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 68)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 57)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 106)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 85)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 38)
Drupal\webprofiler\StackMiddleware\WebprofilerMiddleware->handle(Object, 1, 1) (Line: 52)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 693)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)
require('/var/www/drupal/app/index.php') (Line: 4)

I just created new node type and enable layout builder for it. Then I created a node with layout override.

My env:

Installation profile: Minimal (minimal-8.7.1)
Database updates: Up to date
Entity/field definitions: Up to date
PHP: 7.2.13
It's not clean drupal setup.