Recently, dismissing new topics hasn’t been fully dismissing them, as they still show the blue “new” dot in the Categories view. I’ve seen this consistently on community.wanikani.com, and I just reproduced here as well. Unfortunately you can only see it when one of the dismissed new topics happens to be within the three most recent topics in a category.
To reproduce, first dismiss new topics from the New view. Then go to the Categories view until you see a blue dot next to a topic you just dismissed.
All of this was on mobile. I have no idea if this can happen on desktop as well.