In the process of fleshing out revocation features in my client, I think I may have stumbled onto a bug in Boulder that prevents revocation for certs that are past their associated order's expiration. I submitted issue #5415 about it, but I'd love to get some more data to confirm it's not just my client or a specific bad order.
If you've got any spare orders lying around that are expired, but whose certs are not yet expired, try to revoke them and let me know what happens either here or on the issue.
Any chance that your problem is related to the staging data reset? If your staging order was from before March 2, your order isn't in the staging database anymore.
Ooh, yes!. For some reason I had it in my brain that the staging reset was in January. This particular order expired like a day after the staging reset which means it was created sometime before the reset and likely wiped.