That sounds good!, I think you should check your plugin and make sure the ids are deleted from that object, it seems like this code should do it not sure why it wasn't cleared when you deleted all users.
How to delete resources of 404
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This is a sad song, I forgot to backup the avatars and pictures uploaded by the user.
So I loss them all, and now them will be 404 when openning my site.I only know about deleting fields of 404 in the database, but this workload is too much.
Who can tell me how to delete resources of 404 efficiently, thanks a lot.