It’s a known issue on the lemmy-ui project page in GitHub. Hopefully it will be fixed and merged soon.

Are the reports showing you posts other people reported?

I also recently had an issue where a post from a different Lemmy instance somehow got posted to my community. I reported it, and the admin messaged me asking why I had gone to his instance and reported it. I said it was posted on this instance, not his, but he saw it posted on the other instance.

So, I think possibly with the migration of lemmy.world that some of the posts were getting cross-posted to the wrong lemmy instance and then users would report the posts.