Does not work if blocks are translatable/have a reference field to a user

When trying to add a section containing an inline block to the library, a 500 error occurs:

An AJAX HTTP error occurred.
HTTP Result Code: 500
Debugging information follows.
Path: /section_library/add/section/overrides/node.21/0?_wrapper_format=drupal_dialog.off_canvas&ajax_form=1
StatusText: Internal Server Error
ResponseText: The website encountered an unexpected error. Please try again later.Drupal\Core\Entity\EntityStorageException: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry 'admin-en' for key 'user__name': INSERT INTO {users_field_data} ("uid", "langcode", "preferred_langcode", "preferred_admin_langcode", "name", "pass", "mail", "timezone", "status", "created", "changed", "access", "login", "init", "default_langcode") VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3, :db_insert_placeholder_4, :db_insert_placeholder_5, :db_insert_placeholder_6, :db_insert_placeholder_7, :db_insert_placeholder_8, :db_insert_placeholder_9, :db_insert_placeholder_10, :db_insert_placeholder_11, :db_insert_placeholder_12, :db_insert_placeholder_13, :db_insert_placeholder_14); Array
(
[:db_insert_placeholder_0] => 9
[:db_insert_placeholder_1] => en
[:db_insert_placeholder_2] => en
[:db_insert_placeholder_3] => 
[:db_insert_placeholder_4] => admin
[:db_insert_placeholder_5] => $S$E7N9uvyKaZBP8jpy1Jfy3usstbyhTfpyPrkq50eSYTNrbSoLCtwh
[:db_insert_placeholder_6] => sites@example.com
[:db_insert_placeholder_7] => Europe/Brussels
[:db_insert_placeholder_8] => 1
[:db_insert_placeholder_9] => 1611759379
[:db_insert_placeholder_10] => 1611759488
[:db_insert_placeholder_11] => 1611842998
[:db_insert_placeholder_12] => 1611759692
[:db_insert_placeholder_13] => sites@example.com
[:db_insert_placeholder_14] => 1
)
in Drupal\Core\Entity\Sql\SqlContentEntityStorage->save() (line 810 of core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorage.php). Drupal\Core\Database\StatementWrapper->execute(Array, Array) (Line: 826)
Drupal\Core\Database\Connection->query('INSERT INTO {users_field_data} ("uid", "langcode", "preferred_langcode", "preferred_admin_langcode", "name", "pass", "mail", "timezone", "status", "created", "changed", "access", "login", "init", "default_langcode") VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3, :db_insert_placeholder_4, :db_insert_placeholder_5, :db_insert_placeholder_6, :db_insert_placeholder_7, :db_insert_placeholder_8, :db_insert_placeholder_9, :db_insert_placeholder_10, :db_insert_placeholder_11, :db_insert_placeholder_12, :db_insert_placeholder_13, :db_insert_placeholder_14)', Array, Array) (Line: 97)
Drupal\Core\Database\Driver\mysql\Connection->query('INSERT INTO {users_field_data} ("uid", "langcode", "preferred_langcode", "preferred_admin_langcode", "name", "pass", "mail", "timezone", "status", "created", "changed", "access", "login", "init", "default_langcode") VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3, :db_insert_placeholder_4, :db_insert_placeholder_5, :db_insert_placeholder_6, :db_insert_placeholder_7, :db_insert_placeholder_8, :db_insert_placeholder_9, :db_insert_placeholder_10, :db_insert_placeholder_11, :db_insert_placeholder_12, :db_insert_placeholder_13, :db_insert_placeholder_14)', Array, Array) (Line: 32)
Drupal\Core\Database\Driver\mysql\Insert->execute() (Line: 1011)
Drupal\Core\Entity\Sql\SqlContentEntityStorage->saveToSharedTables(Object) (Line: 949)
Drupal\Core\Entity\Sql\SqlContentEntityStorage->doSaveFieldItems(Object, Array) (Line: 27)
Drupal\user\UserStorage->doSaveFieldItems(Object) (Line: 622)
Drupal\Core\Entity\ContentEntityStorageBase->doSave(NULL, Object) (Line: 452)
Drupal\Core\Entity\EntityStorageBase->save(Object) (Line: 801)
Drupal\Core\Entity\Sql\SqlContentEntityStorage->save(Object) (Line: 339)
Drupal\Core\Entity\EntityBase->save() (Line: 130)
Drupal\section_library\Form\AddSectionToLibraryForm->cloneReferencedEntities(Object) (Line: 92)
Drupal\section_library\Form\AddSectionToLibraryForm->cloneAndReplaceSectionComponents(Object) (Line: 63)
Drupal\section_library\Form\AddSectionToLibraryForm->deepCloneSection(Object) (Line: 149)
Drupal\section_library\Form\AddSectionToLibraryForm->submitForm(Array, Object)
call_user_func_array(Array, Array) (Line: 113)
Drupal\Core\Form\FormSubmitter->executeSubmitHandlers(Array, Object) (Line: 51)
Drupal\Core\Form\FormSubmitter->doSubmitForm(Array, Object) (Line: 593)
Drupal\Core\Form\FormBuilder->processForm('section_library_add_section_to_library', Array, Object) (Line: 321)
Drupal\Core\Form\FormBuilder->buildForm(Object, Object) (Line: 73)
Drupal\Core\Controller\FormController->getContentResult(Object, Object)
call_user_func_array(Array, Array) (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 573)
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: 158)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 80)
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: 52)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 706)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

I was confused because there was no reference field to a user on the block. So did some debugging, and the culprit is the content_translation_uid field. Although the same error would occur if the site builder adds a normal user entity reference field to a block.

My suggestion is to exclude cloning user objects during the deep clone. Either keep the original entity reference, or empty the field. Probably best to keep the original reference.