Magento 2 – Category error : Item (Magento\Catalog\Model\Category\Interceptor) with the same ID “100” already exists

It looks like the category page asks the URL rewrite table for the URL’s. It generates this query:

SELECT `e`.*, 
   IF(at_is_active.value_id > 0, at_is_active.value, 
   at_is_active_default.value) AS 
   `is_active`, 
   `url_rewrite`.`request_path` 
FROM   `catalog_category_entity` AS `e` 
   INNER JOIN `catalog_category_entity_int` AS `at_is_active_default` 
           ON ( `at_is_active_default`.`entity_id` = `e`.`entity_id`) 
              AND ( `at_is_active_default`.`attribute_id` = '43' ) 
              AND `at_is_active_default`.`store_id` = 0 
   LEFT JOIN `catalog_category_entity_int` AS `at_is_active` 
          ON ( `at_is_active`.`entity_id` = `e`.`entity_id` ) 
             AND ( `at_is_active`.`attribute_id` = '43' ) 
             AND ( `at_is_active`.`store_id` = 0 ) 
   LEFT JOIN `url_rewrite` 
          ON ( url_rewrite.entity_id = e.entity_id ) 
             AND ( url_rewrite.is_autogenerated = 1 
                   AND url_rewrite.store_id = 1 
                   AND url_rewrite.entity_type = 'category' ) 
WHERE  ( IF(at_is_active.value_id > 0, at_is_active.value,   
     at_is_active_default.value) 
            = 
            '1' ) 
   AND ( `e`.`entity_id` IN( '100','101') ) 
ORDER  BY `e`.`position` ASC 

But if your url_rewrite-table is corrupted (which is most likely in my case), it ends up with having duplicate ID’s.