What are you using for traffic/download analytics? Google analytics is extremely untrustworthy when it comes to reporting certain sorts of stuff, and I'm not saying this because I have a chip against that evil megacorporation (although I do), I say this because it's the truth. GA is a turd when it comes to reporting on downloads and there have even been cases where just having software DLC on a site can lead to Google Search Console re-classifying your site as a malware distributor/bad website/warez portal.
Here on Itch.io that won't be an issue (I mean the part about getting blacklisted by Google Search) but if you're using GA to report on downloads or product key usage, you may want to rethink your strategy. If you're using the Itch.io interface itself then I can't help you; the only experience I have of such a similar issue is when I intentionally download my own projects again and again in order to share a project deliverable among multiple machines. That bumps my download numbers in a way that might confuse me, later on. Also, testing downloads does number bumping too, in my experience.