Look in wp_usermeta and look for rows which point to a user id that no longer exists in wp_users and delete those rows.
MAKE A BACKUP FIRST!
]]>Take a deep breath and carefully follow this guide. When you’re done, you may want to implement some (if not all) of the recommended security measures.
If you’re unable to clean your site(s) successfully, there are reputable organizations that can clean your sites for you. Sucuri and Wordfence are a couple.
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