Sometimes users submit some content (post or comment), and due to a bug or performance issue the content doesn't appear, even if the instance already saved it. So the user resubmits it over and over... like this:
(This is not my own comment, but I had this issue already.)
While this isn't usually done for the sake of spam, it's still a source of noise for the community, and annoying for the user oneself.
So my suggestion is that, when a user tries to submit a piece of content to Lemmy, Lemmy should compare it with the last piece of content already submitted. And if they're identical, prevent it with some error "warning: duplicate" or similar.