Site error when move a third-level child to a second-level

Hello,

I have found this problem in my site: when I try to move a third level child to a second level. That's a simple schema:

- A
---- A1
---- A2
---- A3
-------- A3-1
-------- A3-2
-------- A3-3

If I move my A3 children between them, I have no problem, but if I try to move A3-1 to the same level of A3, and then click save I'll get this error:
"The website encountered an unexpected error. Please try again later.Drupal\Core\Entity\EntityStorageException: Plugin ID 'taxonomy_menu.menu_link:taxonomy_menu.menu_link.menu_aria_condizionata.67' was not found. in Drupal\Core\Entity\Sql\SqlContentEntityStorage->save() (line 829 of core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorage.php)."

In log messages I found also this:
"Drupal\Component\Plugin\Exception\PluginNotFoundException: Plugin ID 'taxonomy_menu.menu_link:taxonomy_menu.menu_link.menu_aria_condizionata.67' was not found. in Drupal\Core\Menu\MenuLinkManager->getDefinition() (linea 207 di /var/www/clients/client2/web22/web/web/core/lib/Drupal/Core/Menu/MenuLinkManager.php)."

"menu_aria_condizionata" is a menu created with Taxonomy Menu, but anyway I don't try to change the specific taxonomy terms used by that menu, but other terms of the same Vocabulary.

I've recently made the update to drupal 8.5.1, but I can't say if the problem existed before the update or not.

Can anyone help me with this? I tried to search but can't able to find nothing related with this problem.

Thank's in advance.