While scrolling deep through Unknown in grid view, I often notice the same observation appears multiple times. It seems to happen around where I scroll to the bottom and a new batch of observations is fetched.
ex: https://www.inaturalist.org/observations?page=7&place_id=any&subview=grid&iconic_taxa=unknown - scroll down and when new observations appear, you should see a few images that are duplicates. if you hover over them, the URLs are the same. I’m using Chrome.