updates to collection project rules sometimes take a while to save, and if you leave the page while it’s still saving and initiate another change, you can end up with duplicates. i think if you have multiple people making changes at the same time, you can also end up with duplicates. (here’s a previous case where we noted some duplicates: https://forum.inaturalist.org/t/add-user-function-working-properly/22132/10).
i don’t think the duplication actually causes any specific issues other than clutter. you should be able to delete the duplicates without any issue, too.