States - The website encountered an unexpected error. Please try again later.

Even I've faced the same issue with workflow.

The website encountered an unexpected error. Please try again later.

Drupal\Core\Entity\EntityStorageException: 'workflow_config_transition' entity with ID 'review_bookk' already exists. in Drupal\Core\Entity\EntityStorageBase->doPreSave() (line 430 of core/lib/Drupal/Core/Entity/EntityStorageBase.php).
Drupal\Core\Entity\EntityStorageBase->save(Object)
Drupal\Core\Config\Entity\ConfigEntityStorage->save(Object)
Drupal\Core\Entity\Entity->save()
Drupal\Core\Config\Entity\ConfigEntityBase->save()
Drupal\workflow\Entity\WorkflowConfigTransition->save()
Drupal\workflow\Entity\Workflow->createTransition('save_book', 'approve_book')
Drupal\workflow_ui\Form\WorkflowConfigTransitionRoleForm->buildRow(Object)
Drupal\workflow_ui\Form\WorkflowConfigTransitionFormBase->buildForm(Array, Object)
Drupal\workflow_ui\Form\WorkflowConfigTransitionRoleForm->buildForm(Array, Object)
call_user_func_array(Array, Array)
Drupal\Core\Form\FormBuilder->retrieveForm('workflow_config_transition_permission_form', Object)
Drupal\Core\Form\FormBuilder->buildForm(Object, Object)
Drupal\Core\Form\FormBuilder->getForm(Object)
Drupal\workflow_ui\Controller\WorkflowConfigTransitionListBuilder->render()
Drupal\Core\Entity\Controller\EntityListController->listing('workflow_config_transition')
call_user_func_array(Array, Array)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}()
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}()
call_user_func_array(Object, Array)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1)
Stack\StackedHttpKernel->handle(Object, 1, 1)
Drupal\Core\DrupalKernel->handle(Object)

See #2696001: Unable to go to states tab, caused by workflow_devel_workflow_operations()