Kodi stores artwork path references in its database table 'art'. Truncating this table and running Artwork Downloader, refreshes all of your art.

Step-by-step guide:

• Close Kodi on all applicable devices
• Make sure you have a backup of your database
• Connect to your database
  • If you are using shared libraries via MySQL, use a MySQL client to connect to the database. Make sure to “use MyVideos<DBNUM>;” on the correct database. If you are unsure which version this is, check your kodi.log file.
  • If you are using local databases, download an SQLite client (like DB Browser for SQLite)
• Select your database and run the SQL query

  truncate table 'art';

• Delete the Thumbnails folder under the userdata folder
• Delete the Textures<DBNUM>.db file from the userdata/Databases folder
• Start Kodi
• Run Artwork Downloader