Your site has been upgraded from joomla 3 unsuccessfuly or that you have copied articles directly from another site using the database

workflow.sql

-- A upgrade from 3 to 4 (or copy manually the content table) was not completed successfuly 
-- as it should have created a record for each article in the #_workflow_associations table. (even if you are not using workflows it needs a record in that table). 
-- Newly created articles in j4 or higher have that record created automatically.  
-- The sql query below should create the missing records for you. 
--
-- replace #_ with your own db prefix

INSERT INTO #__workflow_associations (item_id, stage_id, extension) 
SELECT c.id as item_id, '1', 'com_content.article' FROM #__content AS c 
WHERE NOT EXISTS (SELECT wa.item_id FROM #__workflow_associations AS wa WHERE wa.item_id = c.id);