Stock messages app showing incorrect (?) number on home screen notification dot/bubble

I have a Samsung Galaxy S9 running Oreo and my question is I assume related to the new notification functionality that came in since the previous version. Everytime I receive a new SMS into the stock Samsung messages app, it shows 7 in the notifcication bubble/dot on the home screen, but I have only received/have 1 unread message. When I actually do have multiple unread messages, the number goes up disproportionately again. I can't get my head around it, can someone please explain.

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