Hi Mike,
I found example of duplicating CampaignSharedSets in 2020 year in account 9988987723, campaign
6518371350.

That is how it looks on UI, only the most recent CampaignSharedSet should still exist - GOOGLE_MKTG_NEGATIVE_KEYWORDS - EN - 20200418-021841 - R16, as a result the other 2 are duplicated and it means they are applied to Removed SharedSets.
I'll give you info about this one GOOGLE_MKTG_NEGATIVE_KEYWORDS - EN - 20200111-011216 - R16 because it's the most recent one.

As you can see on the screen CampaignSharedSet is
Enabled and is attached to SharedSet with id
6594099514 which has
Removed status.
Hope it will help you to find out what can happened, because I saw a lot of such examples even in this year.