I migrated data from magento 1.x to 2.x and all things was good.
But when we tried to update a category, it says "URL key for specified store already exists." and data is not saved. But it's not for all categories. Only some categories couldn't be saved.
So I run a mysql command(delete from url_rewrite where entity_type='category' ) and mage2 command(bin/magento indexer:reindex).
But the problem is still teasing me.