Hello.
That is something I thought I wouldn't have to make a topic about, since I thought it was fairly resolved back in August/September when I was noticing this, but apparantly it didn't help that much.
But apparantly, there are multiple users who don't think that it is necessary to add a source to their uploads, the post where this issue came back was post #2572099 where I asked what the source is of that upload.
And evazion found the source pretty easy with this tool and it is also suggested that one should always add a source to their uploads in the howto:upload wiki. If the source can't be remembered that one should use the extension that evazion used to find the post. If all that doesn't help, then it should be mandatory to add source_request to the upload. But to leave the source field just blank isn't that good, but there might be some exception where the source can't be easil determined, like image boards or Patreon rewards.
Anyways, sourcing uploads is pretty important, since we are a reposting site.