PluginNotFoundException is thrown for a custom created page

PluginNotFoundException is thrown for a custom page route when module is upgraded from metatag-8.x-1.0-beta10 to metatag-8.x-1.0-beta 11.
Ran "drush updb " and cleared cache. Still exception is thrown. There were no DB updates for the updated version of the module.

Following is the backtrace information for the exception -

Drupal\Component\Plugin\Exception\PluginNotFoundException: The "custom_page" entity type does not exist. in Drupal\Core\Entity\EntityTypeManager->getDefinition() (line 133 of core/lib/Drupal/Core/Entity/EntityTypeManager.php).
metatag_get_route_entity() (Line: 333)
metatag_get_default_tags() (Line: 286)
metatag_get_tags_from_route() (Line: 93)
metatag_page_attachments(Array) (Line: 297)
Drupal\Core\Render\MainContent\HtmlRenderer->invokePageAttachmentHooks(Array) (Line: 273)
Drupal\Core\Render\MainContent\HtmlRenderer->prepare(Array, Object, Object) (Line: 117)
Drupal\Core\Render\MainContent\HtmlRenderer->renderResponse(Array, Object, Object) (Line: 90)
Drupal\Core\EventSubscriber\MainContentViewSubscriber->onViewRenderArray(Object, 'kernel.view', Object) (Line: 111)
Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch('kernel.view', Object) (Line: 149)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 64)
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: 99)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 78)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 50)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 652)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)