I've sent Gravy the full list of affected transactions so far, here

There is a common pattern. It appears that all previous attempts by the same donors were refused for various reasons (e.g., insufficient funds, expired card, suspected fraud), and the donor has subsequently reattempted, but Adyen has detected it's a retry and applied the earlier block. I wonder if Adyen are sending back a "new" rejection message to Gravy due to this case, and Gravy needs to update their mappings.

Gravy has released a fix for this.

Amber spotted a new instance today where Gravy did not pick up a fraud rejection code, so I reopened the item on the Gravy tracker.