It’s possible that Media Cleaner refuses to clean certain media because they are either unsafe to delete or the physical files are already missing. In those cases, the plugin will display an error message and ask you to run a new scan, which is the recommended course of action.
If this issue persists and prevents you from emptying the trash, you can go to the Advanced Settings and use the Force Clean Trash option. This will identify all items in the trash that are returning errors and permanently remove them.
Before using this feature, make sure you have a backup.

Please note that this action is irreversible. The affected media will be permanently deleted and cannot be recovered afterward.
Manual Removal
You can check under your /uploads folder to see if there’s a trash folder containing the media.
If it’s missing, it’s likely that the files have already been deleted manually or by another process, meaning the space shown as being used by the trash is actually 0. This happens when your database isn’t up to date with the actual state of the folder.
To fix this, you can run the following SQL query in your database (always make a reliable backup first):
DELETE FROM wp_mclean_scan WHERE deleted = 1
Most database admin panels have a section where you can manually run SQL queries — simply paste this code there and execute it.
If you’re not sure where that is, your hosting provider can guide you.
If the trash folder still exists and contains files, you can manually delete it, then run the same SQL query to update the database afterwards.